System for producing a fully impregnated thermoplastic prepreg

ABSTRACT

A system for manufacturing a thermoplastic prepreg includes a double belt mechanism that is configured to compress a fiber mat, web, or mesh that is passed through the double belt mechanism, a resin applicator that is configured to apply monomers or oligomers to the fiber mat, web, or mesh, and a curing oven that is configured to effect polymerization of the monomers or oligomers and thereby form the thermoplastic polymer as the fiber mat, web, or mesh is moved through the curing oven. The double belt mechanism compresses the fiber mat, web, or mesh and the applied monomers or oligomers as the fiber mat, web, or mesh is passed through the curing oven so that the monomers or oligomers fully saturate the fiber mat, web, or mesh. Upon polymerization of the monomers or oligomers, the fiber mat, web, or mesh is fully impregnated with the thermoplastic polymer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 15/944,249 filed Apr. 3, 2018, entitled “SYSTEM FOR PRODUCING AFULLY IMPREGNATED THERMOPLASTIC PREPREG,” which is a continuation ofU.S. application Ser. No. 14/794,634 filed Jul. 8, 2015, entitled“SYSTEM FOR PRODUCING A FULLY IMPREGNATED THERMOPLASTIC PREPREG,”, nowU.S. Pat. No. 9,993,945 issued Jun. 12, 2018, the entire disclosures ofwhich are hereby incorporated by reference, for all purposes, as iffully set forth herein. This application is also related to U.S. patentapplication Ser. No. 14/088,034 filed Nov. 22, 2013, and titled“FIBER-CONTAINING PREPREGS AND METHODS AND SYSTEMS OF MAKING,” theentire disclosure of which is hereby incorporated by reference, for allpurposes, as if fully set forth herein.

BACKGROUND

The use of fiber-reinforced composites is growing in popularity withapplications in transportation, consumer goods, wind energy, andinfrastructure. Some of the many reasons for choosing composites overtraditional materials such as metals, wood, or non-reinforced plasticsinclude reduced weight, corrosion resistance, and improved mechanicalstrength. Within the field of fiber-reinforced polymeric composites,thermoplastics are increasingly being used in place of thermosets as thematrix resin due to better durability, recyclability, thermoformability,improved throughput, lower material cost, and lower manufacturing cost.

Many continuous fiber reinforced thermoplastic composites are producedfrom impregnated tapes. These impregnated tapes may be unidirectionalfiber tapes that are impregnated with a thermoplastic resin. These canbe layered and thermoformed to produce a wide variety of composites ofthe desired shape and strength. There are significant challengesassociated with producing impregnated tapes at low cost and highquality. Traditionally thermoplastic resins are melted and applied tofibers, but molten thermoplastic resins have very high viscosity and,when combined with the high fiber content that is desired, results inincomplete resin impregnation and/or low throughput. What is desired isa continuous manufacturing process with high throughput that producesfully impregnated thermoplastic prepregs without defects and goodcoupling between the fibers and the matrix resin. For the conventionalpartially impregnated thermoplastic prepregs, high pressure is needed inthe consolidation step to promote additional impregnation, whichintroduces excessive flow of the resin matrix and causes detrimentalchanges in fiber orientation in the finished parts. The fullyimpregnated thermoplastic prepregs of the instant invention areadvantageous in achieving the desired properties in final compositeparts, as no additional impregnation is needed in the consolidationstep.

BRIEF SUMMARY

The embodiments described herein provide fully impregnated thermoplasticprepreg products, and specifically systems and methods for making thesame. According to one aspect, a system for manufacturing athermoplastic prepreg includes a double belt mechanism that includes anupper belt and a lower belt. The upper belt is positioned atop the lowerbelt to compress a fiber mesh that is passed through the double beltmechanism. The lower belt has a longitudinal length that issubstantially longer than the upper belt. The system also includes adrying mechanism that is positioned atop the lower belt and that isconfigured to remove residual moisture from the fiber mesh as the fibermesh is moved past the drying mechanism. The system further includes aresin application die that is positioned atop the lower belt and that isconfigured to apply monomers or oligomers to the fiber mesh as the fibermesh is moved past the resin application die. The monomers or oligomersare polymerizable to form a thermoplastic polymer. The systemadditionally includes a curing oven that is configured to effectpolymerization of the monomers or oligomers and thereby form thethermoplastic polymer as the fiber mesh is moved through the curingoven. The fiber mesh includes chopped fibers and the double beltmechanism is configured to compress the fiber mesh and the appliedmonomers or oligomers as the fiber mesh is passed through the curingoven so that the monomers or oligomers fully saturate the fiber mesh andthe fiber mesh is fully impregnated with the thermoplastic polymer uponpolymerization of the monomers or oligomers.

According to another aspect, a method of forming a thermoplastic prepregincludes moving a fiber mesh atop a lower belt of a double belt pressmechanism and drying the fiber mesh via a drying mechanism that ispositioned atop the lower belt to remove residual moisture from thefiber mesh. The method also includes applying monomers or oligomers tothe fiber mesh via a resin application die that is positioned atop thelower belt and passing the fiber mesh and the applied monomers oroligomers between the lower belt and an upper belt of the double beltpress mechanism to press the monomers or oligomers through the fibermesh and thereby fully saturate the fiber mesh with the monomers oroligomers. The method further includes passing the fully saturated fibermesh through a curing oven that is configured to polymerize the monomersor oligomers as the fiber mesh is moved through the curing oven andthereby form the thermoplastic polymer. The fiber mesh includes choppedfibers and the fiber mesh is fully impregnated with the thermoplasticpolymer upon polymerization of the monomers or oligomers.

According to yet another aspect, a thermoplastic prepreg includes a webor mesh of fibers and a thermoplastic material that fully impregnatesthe web or mesh of fibers. The web or mesh of fibers includes choppedfibers having a fiber length and a fiber diameter. The chopped fibersare un-bonded such that the web or mesh of fibers is not mechanicallybonded and does not include a binder other than the thermoplasticmaterial that binds the chopped fibers together. The thermoplasticprepreg has a void content of less than 5% and includes between 5 to 95weight percent of the thermoplastic material. The thermoplastic materialincludes or consists of polymers that are formed by in-situpolymerization of monomers or oligomers in which greater than 90% byweight of the monomers or oligomers react to form the thermoplasticmaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

The present technology is described in conjunction with the appendedfigures:

FIGS. 1A and 1B illustrate systems that may be used to produce prepregsthat are fully impregnated with a thermoplastic polymer.

FIG. 2 illustrates a method of forming a fully impregnated thermoplasticprepreg product.

FIG. 3 illustrates another method of forming a fully impregnatedthermoplastic prepreg product.

FIG. 4 illustrates a SEM micrograph of a cross-section of a fullyimpregnated polyamide-6 prepreg.

FIGS. 5-8 illustrate systems that may be used to produce prepregs thatare fully impregnated with a thermoplastic polymer.

FIG. 8A illustrates a system in which a fiber chopper is replaced with afiber scattering unit.

FIG. 8B illustrates a system that includes a winding mechanism thatwinds a fully cured chopped fiber thermoplastic prepreg into a rollproduct.

FIGS. 9-13 illustrate exemplary prepregs that are fully impregnated witha thermoplastic polymer.

FIG. 14 illustrates another method of forming a fully impregnatedthermoplastic prepreg product.

FIGS. 15-16 illustrates a system that includes an alternative means ofdelivering a reactive resin to a resin application mechanism.

FIGS. 17-20 illustrates embodiments of extruders that may be used todeliver a reactive resin to a resin application mechanism.

In the appended figures, similar components and/or features may have thesame numerical reference label. Further, various components of the sametype may be distinguished by following the reference label by a letterthat distinguishes among the similar components and/or features. If onlythe first numerical reference label is used in the specification, thedescription is applicable to any one of the similar components and/orfeatures having the same first numerical reference label irrespective ofthe letter suffix.

DETAILED DESCRIPTION

The embodiments described herein relate to fully impregnatedthermoplastic prepreg products, and specifically systems and methods formaking the same. The prepreg products are fully impregnated withthermoplastic materials that allow the prepreg products to be reheatedand molded into a given shape. The prepreg products are made usingreactive resin materials, specifically monomers and oligomers. Forexample, in an exemplary embodiment the resin material is caprolactam,which is extremely sensitive to moisture, wherein even a small amount ofmoisture can affect the anionic polymerization of the caprolactam.Because of the high moisture sensitivity of these materials, achieving ahigh conversion rate of the reactive resin materials to polymers is verydifficult.

In order to achieve a commercially viable prepreg product using monomeror oligomer materials (hereinafter resins, reactive resins, or resinmaterials), the conversion of the reactive resin to a polymer needs tobe greater than 90% by weight and more commonly greater than 95% byweight. A person of skill in the art would recognize, the conversion ofthe reactive resin to a polymer may be readily determined. For example,a residual monomer or oligomer content in the prepreg can be measuredvia a solvent extraction method, which is described herein below.Specifically, when caprolactam is used as the reactive resin, the amountof residual caprolactam in a polyamide-6 (PA-6) prepreg can be measuredvia the extraction of caprolactam from a powder of grounded prepregusing hot water. The conversion of the reactive resin can be deducedbased on the residual monomer or oligomer content. High molecularweights of the thermoplastic polymers are also typically desired. Inpreferred embodiments the resin material comprises caprolactam. Thereactive resin material comprising caprolactam is extremely sensitive tomoisture. The presence of moisture can stop or interfere with theanionic polymerization of caprolactam into a polyamide-6 polymer. Forexample, a moisture content of greater than 200 ppm in the resin cansignificantly interfere with the polymerization process and lower theconversion of the caprolactam material to below 90% by weight. The term“substantially moisture-free” or “substantially zero” in references tohumidity recognizes that some level or amount of humidity may be presentin the air. However, as used herein the term implies that any humiditypresent in the air is negligible, minor, insignificant, or otherwiseinconsequential. For example, a “substantially moisture-free”environment may be created by employing a moisture purge mechanism thatis operable to maintain the relatively humidity in the environment to bebelow 1% under the temperature range of 5-35° C.

The systems and methods described herein are useful for manufacturingprepreg products using reactive resin materials. The resin conversionrate that is achieved via the systems and methods described herein isgreater than 90% by weight and more commonly greater than 95% by weight.In most embodiments, the conversion rate of the resins is greater than98% by weight or even greater than 99% by weight. As described herein,thermoplastic polymers in the prepreg products are formed via in-situpolymerization, which is not a common technique in manufacturingthermoplastic prepreg products. In addition, the systems and methodsdescribed herein are able to achieve this high conversion rate utilizinga continuous process, wherein a fabric or mat material (woven ornonwoven) is essentially moved constantly or continually throughout themanufacturing process. The continuous process greatly increases theefficiency of the manufacturing process, which decreases the overallcost of the final prepreg product. For example, the manufacturing timebetween coating of the reactive resin (e.g., caprolactam) to theformation of a fully impregnated thermoplastic prepreg may be less than20 minutes and commonly less than 10 minutes. In many embodiments, thisprocessing time may be less than 5 minutes.

The systems and methods described herein are also able to achieve fulland complete impregnation of the prepreg with the thermoplastic polymer.It should be realized that the term “reactive resin” may be used inplace of the term monomers and/or monomers or oligomers within thedescription and/or claims as desired. The viscosity of the reactiveresin at the time when it is applied to a fabric or mat is lower than500 mPa-s, typically lower than 100 mPa-s and more commonly lower than10 mPa-s. The low viscosity of the reactive resin allows the resin toflow within and fully saturate either a single layer of the fabric ormat, or multiple layers of these materials. Accordingly, the systems andmethods described herein are capable of producing prepregs that includemultiple layers of materials with each layer being fully saturated orimpregnated with the thermoplastic polymer materials. The final prepregproduct can be made flexible with high content of reinforcing fibers.Because the prepreg products are flexible, the prepregs may be rolledinto a rolled product. In other embodiments, the prepreg may be cut intoindividual sheets having any desired length or width.

The embodiments described herein provide a process and apparatus thatutilizes mixing of reactive resin components, followed by application ofthe reactive resin components to a fabric or mat, which may be formedfrom the various fiber materials described herein. The reactive resincomponents are then cured in an oven to form a fully impregnated prepreghaving a thermoplastic polymer matrix. In a specific embodiment,caprolactam is polymerized to form polyamide-6 in the finished prepreg.The system is designed to isolate the reactive resin components fromatmospheric moisture in order to achieve high conversion from monomer topolymer. Specifically, the system is designed to ensure a substantiallymoisture-free environment in the vicinity of the reactive resin coatedfabric or mat (woven or nonwoven). The systems and methods describedherein are designed to isolate the reactive components from atmosphericmoisture in order to achieve high conversion from monomer to polymer.This is achieved, in part, by controlling the environment in thevicinity of the production process and/or by removing residual moisturefrom the fabric or mat (woven or nonwoven) and/or any of the processingsystems.

As used herein, the reactive resin means the resin materials thatcomprise monomers or oligomers capable of polymerizing to formthermoplastic polymers. The reactive resins may include lactams such ascaprolactam and laurolactam and lactones. In an exemplary embodiment,the reactive resin comprises caprolactam. In some embodiments, mixturesof monomers and/or oligomers may be used. For example, mixture ofcaprolactam and laurolactam may be used, which will copolymerize in thecuring oven to form copolymers with tailored properties. As used herein,the activator may be any material that activates and accelerates thepolymerization of monomers or oligomers. Exemplary activators for theanionic polymerization of caprolactam include blocked isocyanates andN-acylcaprolactams. As used herein, the catalyst may be any materialthat catalyzes the polymerization of monomers or oligomers. Exemplarycatalysts for the anionic polymerization of caprolactam include alkalinesalt of caprolactam such as sodium caprolactamate.

In some embodiments, it may be desirable to add a toughening agent, suchas a rubber material, to further toughen the thermoplastic polymer. Theterm “toughening” a polymer refers to the ability of the polymericsubstance to absorb energy and plastically deform without fracture.Adding a toughening agent increases the ability of the thermoplasticpolymer to plastically deform without fracture. For many engineeringapplications, material toughness is a deciding factor in final materialselection. In regards to the prepregs formed via in situ polymerizationof caprolactam, rubber toughening of polyamide-6 thermoplastic prepregsis a process in which a rubber phase is introduced into a polyamide-6matrix resin to increase the toughness or mechanical robustness of thethermoplastic prepreg. Thermoplastic prepregs containing rubbermodifiers have high impact resistance and abrasion resistance; and aresuitable for demanding applications such as those requiring lowtemperature impact resistance.

Several methods may be employed to add a toughening agent or componentto the reactive resin. For example, elastomeric prepolymer activators,such as Nyrim® prepolymer activators from Bruggemann (NYRIM® P1-30Prepolymer, NYRIM® P1-20A Prepolymer), may be used to form blockcopolymers consisting of an elastomeric block and a hard polyamide-6block. The elastomeric block of the copolymer functions as toughener andimpact modifier. Alternatively, rubbery particles may be used asadditives or fillers in the polyamide-6 resin matrix to toughen thematrix resins. Core-shell rubber (CSR) particles, which consist of asoft rubbery core and a harder shell, may be used as the toughener forpolyamide-6 resin matrix. Common core materials may be based onbutadiene, siloxane, or acrylic.

Various terms are used herein to describe fiber-based products. Forexample, the term “fabric” is used in the application to describe wovenfabrics and stitch-bonded non-crimp fabrics. The application includesthe following terms to describe fiber-based nonwoven products: mat, web,mesh, and the like. It should be understood that these terms may be usedinterchangeably in the embodiments. Unless specifically claimed, thedisclosure is not limited to any one particular fiber-based product.Accordingly, it is contemplated that the terms may be replaced orchanged in any of the embodiments described without departing from theintended scope of description. Furthermore, the term “fiber mat, web, orfabric” or “fiber-based product” may be substituted in the descriptionor claims and is intended to cover any and all fiber-based products orcomponents that are described or contemplated herein.

A common type of fiber that is used in the fabric or mat is glassfibers, although various other fibers could be used such as carbonfibers, basalt fibers, metal fibers, ceramic fiber, natural fibers,synthetic organic fibers such as aramid fibers, and other inorganicfibers. The term fabric or mat as used herein refers to woven ornonwoven materials. The woven materials are materials that are producedby weaving multiple roving strands together. The term roving as usedherein refers to a bundle of fibers that are positioned adjacent oneanother to form a rope, thread, or cord like component. The rovingstrands are commonly woven so that a first plurality of strands extendin a first direction (e.g., weft direction) and a second plurality ofstrands extend in a second direction that is typically orthogonal to thefirst direction (e.g., warp direction). The first plurality of strandsare roughly parallel with one another as are the second plurality ofstrands. The fabrics or cloths may be unidirectional, where all or mostof the roving strands run or extend in the same direction, or may bebidirectional, wherein the roving strands run in two, typicallyorthogonal, directions. Various weaves may be used to form the fabric orcloths described herein, including: plain weaves, twill weaves, satinweaves, multiaxial weaves, or stitch bonding. The cloths or fabrics thatare employed may contain any kind of woven fabric or stitch bondednon-crimp fabric. The fabrics or mats may also contain chopped fibers inaddition to or alternatively from the continuous fibers. The fabrics ormats may be a hybrid from different type of fibers. For ease indescribing the embodiments herein, the embodiments will generally referto the use of glass fibers, although it should be realized that variousother fiber types may be used.

The term mat as used herein refers to nonwoven materials. As brieflydescribed above, nonwoven fiber mats are used in addition to or in placeof the reinforcement fabrics. The nonwoven fiber mats are commonlyformed of fibers that are mechanically entangled, meshed together, orchemically bonded, rather than being woven or stitched in a uniformdirection. The nonwoven fiber mats exhibit more uniform strengthcharacteristics in comparison to the reinforcement fabrics. Stateddifferently, the strength of the nonwoven fiber mats is typically lessdirectionally dependent. In comparison, the strength of thereinforcement fabrics is directionally dependent whereby the fabrics orcloths exhibit substantially more strength in a direction aligned withthe fibers and less strength in a direction misaligned from the fibers.The reinforcement fabrics or cloths are substantially stronger than thenonwoven mats when the tension is aligned with the fibers. For ease indescribing the embodiments herein, the embodiments will generally referto fabrics or mats, which is intended to apply to both fabrics or clothsand nonwoven fiber mats.

The fibers used in the fabrics or mats may be treated with a sizingcomposition including coupling agent(s) that promote bonding betweenreinforcing fibers and polymer resin. For example, the fibers may besized with one or more coupling agents that covalently bond thethermoplastic resin to the fibers. Exemplary coupling agents may includecoupling-activator compounds having a silicon-containing moiety and anactivator moiety. Specific examples of coupling-activator compoundsinclude 2-oxo-N-(3-(triethoxysilyl)propyl)azepane-1-carboxamide.Exemplary coupling agents may also include blocked isocyanate couplingcompounds having a silicon-containing moiety and a blocked isocyanatemoiety. Exemplary coupling agents may also include coupling compoundshaving a functional group that may react with the reactive resin to formcovalent bond. Specific example of the coupling compounds having afunctional group include silane coupling agent having amino, epoxy, orureido functional groups.

The term thermoplastic polymer or material refers to polymers that arecapable of being melted and molded or formed into various shapesmultiple times. As such, the fully impregnated thermoplastic prepregsmay be positioned in a mold and reformed or remolded into variousdesired shapes. Examples of polymer materials or resins that may be usedwith the embodiments herein include polyamides, specifically includingpolyamide-6.

The description and/or claims herein may use relative terms indescribing features or aspects of the embodiments. For example, thedescription and/or claims may use terms such as relatively, about,substantially, between, approximately, and the like. These relativeterms are meant to account for deviations that may result in practicingand/or producing the embodiments described herein. For example, thedescription describes mixtures from two holding tanks as being mixedinto a “substantially homogenous mixture”. The disclosure also describespurging a fabric or mat with “a substantially moisture-free gas” andthat the fabric or mat is in “substantially constant movement” between astarting point and ending point. The term “substantially” is used inthese descriptions to account for small deviations or differences from acomplete homogenous mixture, or a completely moisture-free gas, or anentirely constant movement. For example, a skilled artisan wouldrecognize that the moisture-free gas may include some negligible amountof moisture and that some negligible amount of non-homogeneity may bepresent within the homogenous mixture. The skilled artisan would alsorecognize that some negligible stoppage or non-movement of the fabric ormat may occur without departing from the spirit of the disclosureherein. These deviations of differences may be up to about 10%, but aretypically less than 5%, or even 1%. A similar rationale applies to anyof the other relative terms used herein.

In producing conventional thermoplastic prepregs, the process of fullyimpregnating or saturating the fabric or mat is rather expensive and/ordifficult due to the high melt viscosity of the thermoplastic resin. Insome instances, a solvent is added to the polymer resin/thermoplasticmaterial to reduce the viscosity of the material. While the reducedviscosity may add in fully impregnating the reinforcement fabric or mat,the solvent needs to be subsequently removed from the fabric or matafter the polymer resin/thermoplastic material is impregnated within thefabric or mat. Removal of the solvent commonly involves heating thecoated fabric or mat to evaporate the solvent, adding cost andenvironmental concerns. In contrast to these systems, no solvent is usedin the reactive resin described herein.

Other conventional technologies use pre-impregnated unidirectionalthermoplastic tapes of polymer resin and reinforcing fibers. These tapesare typically manufactured as a single layer by applying a moltenpolymer resin atop flattened rovings. For example, glass rovings may bepassed over rollers to flatten and spread fibers that are then coatedwith a molten polymer resin. The tapes are then cooled with the glassfibers encased within the hardened polymer resin material. The tapes maythen be used in producing other products, typically by stacking andwelding several layers of tape together. The process of spreading fibersfor resin impregnation typically limits to rovings; since spreadingfibers in fabrics or mats is nearly impossible.

In contrast to conventional prepregs, the production of thethermoplastic prepregs described herein is fast and simple. For example,fully saturating the fabric or mat is relatively easy since the reactiveresin materials (e.g., caprolactam) have a low melt viscosity that iscomparable to water. This low viscosity allows the resin materials toeasily flow within and fully saturate a single layer, or multiplelayers, of the fabric or mat. The capillary force of the rovings orfibers further aids in saturating the fabric or mat. The low viscosityof these materials also allows the materials to be applied to aconstantly or continually moving sheet of material. The resins may thenbe converted into a thermoplastic polymer material so that the fabric ormat is fully impregnated with the thermoplastic material.

While the embodiment herein generally refers to the manufacture ofpolyamide-6 prepregs, other reactive resin systems can be easily adaptedto work with the same or similar apparatus to form thermoplasticprepregs including other types of polyamides and blends of thermoplasticpolymers such as the blends of polyamides and polyesters.

Having described several aspects of the embodiments generally,additional aspects will be evident with reference to the description ofthe several drawings provided below.

Systems

Referring now to FIGS. 1A and 1B, illustrated is a system that may beused to produce prepregs that are fully impregnated with a thermoplasticpolymer. The systems of FIGS. 1A and 1B are capable of producing thefully impregnated thermoplastic prepregs in a continuous process,wherein a fabric or mat 4 is continually or constantly in movementthrough the system. Stated differently, the term continuous processmeans that the process is not interrupted or paused in performing anyone process step. Rather, each step in the process is continually orconstantly being performed. For example, the fabric or mat iscontinually moved from a rolled good, coated with the resin material,cured in the oven, and rolled into a final product. In contrast,conventional systems typically are halted or interrupted during theperformance of one or more steps, such as the impregnation of fibroussubstrates with high melt viscosity thermoplastic polymer resin.

In some embodiments, the system includes two vessels or holding tanks(i.e., 1 and 2 2). The holding tanks, 1 and 2, may be heated and purgedwith nitrogen to ensure the removal of any moisture, which couldotherwise reduce the reactivity of the raw materials and consequentlyreduce the conversion of the resins to a polymer. One of the holdingtanks (e.g., holding tank 1) may contain a mixture of a resin and acatalyst. In a specific embodiment, the holding tank (e.g., tank 1)includes caprolactam and a catalyst, such as sodium caprolactamate orany other catalyst. The other holding tank (e.g., tank 2) may contain amixture of the resin and an activator. In a specific embodiment, theother holding tank (e.g., tank 2) includes caprolactam and an activator,such as N,N′-hexane-1,6-diylbis(hexahydro-2-oxo-1H-azepine-1-carboxamide) or anyother activator. The holding tanks, 1 and 2, are heated to a temperaturethat allows the reactants to melt. In some embodiments, the temperaturemay be between about 70 and 120° C. The molten reactants (e.g., theresin and activator or catalyst) have a very low viscosity, for example,lower than 10 mPa-s.

The reactants from the two holding tanks, 1 and 2, are metered into amixer or mixing head 3 that ensures the correct ratio of the resin,activator, and catalyst. In one embodiment, the mixtures from the twoholding tanks, 1 and 2, may be provided to the mixer in a 1/1 ratio. Themixtures from the two holding tanks, 1 and 2, are thoroughly mixed inthe mixer 3 into a substantially homogenous mixture.

In some other embodiments, the system includes single or multiplevessels or holding tanks. Each of the vessels or holding tanks maycontain individual components or mixtures of the reactive resinmaterials. Each of the vessels or holding tanks are heated to atemperature that allows the reactants to melt.

A fabric or mat 4 is unwound or otherwise provided to the system. Thesystem may include a mechanism that unwinds the fabric or mat and movesthe fabric or mat through the system and along or about the variousprocesses. In some embodiments, the mechanism may include poweredrollers or calendars and/or a conveyor system, that move the fabric ormat through the system.

In some embodiments, the activator is included on the surface of thefibers. The fabric or mat may consist of glass fibers that have beenpre-treated with a sizing composition. For example, the sizingcomposition may include a coupling activator that covalently bonds thepolymerization activator moiety to the glass fiber. In such instances,the bonding between the thermoplastic polymer and the fibers may besignificantly strengthened or enhanced. When the fabric or mat includesthe activator, only a single holding tank (e.g., tank 1) containing theresin and catalyst may be used, or a reduce amount of the activator maybe mixed with the resin in the second holding tank (e.g., tank 2). Insome embodiments, two holding tanks, 1 and 2, may be used and eachholding tank may include a different resin material. For example, afirst holding tank 1 may include caprolactam while the second holdingtank 2 includes laurolactam. In such instances, a combination of two ormore types of reactive monomers and/or oligomers may be applied to thefabric or mat.

In a specific embodiment, the fiber sizing contains a mixture of silanecoupling agents, polymeric film formers, and other additives that aredesigned to enhance the interfacial bonding between the glass fiber andpolyamide-6 matrix. Specifically, a reactive silane is used that allowssome of the polymerization to be initiated directly from the glasssurface, thus improving the coupling between the reinforcing fibers andthe resin matrix to improve composite properties.

After the fabric or mat 4 is unwound, or during the unrolling of thefabric or mat, the fabric or mat may be subjected to a drying mechanismthat removes residual moisture from one or more surfaces of the fabricor mat. For example, an infrared heater 5 may be used to raise thetemperature of the fabric or mat and thereby remove any residualmoisture. In a specific embodiment, the infrared heater 5 may bepositioned atop or over the fabric or mat 4 to remove residual moisture.In some embodiments, a second heater can be positioned on an oppositeside (e.g., bottom side) of the fabric or mat 4 to further aid inremoval of residual moisture. In other embodiments, a pre-drying ovenmay be used in place of or in addition to the infrared heater 5. Thepreheating of the fabric or mat 4, and/or the preheating of the resin,may be employed to prevent the monomer/oligomer from solidifying uponcontact with the fibers of the fabric or mat, which may ensure a goodwet out of the resin at higher line speeds.

The resin mixture is then applied to the fabric or mat 4 using a resinapplication die 6 or other resin application mechanism. The resinapplication die 6 may be a slot die. The slot die 6 may be positionedatop or adjacent one or more surfaces of the fabric or mat 4. The resinmixture is typically applied as close as possible to an inlet of thecuring oven 8 in order to minimize exposure of the resin material to thesurrounding air. To minimize exposure to the surrounding air, the slotdie 6 may be positioned directly adjacent to the inlet of the curingoven 8. In some embodiments, the slot of the slot die 6 may have anopening of about 1.0 mm or less that enables the use of a very thin die.The thin die allows the distal end of the die to be positionedsubstantially close to the curing oven 8 to minimize the exposure of theresin mixture to the surrounding environment. In some embodiment, thedistal end of the slot die 6 may be positioned within 1.0 inches of thecuring oven's inlet, and preferably within 0.5 inches of the inlet. Theslot die 6 may be temperature controlled within a temperature rangeabove the melting point of the reactive resin. For the reactive resincomprising caprolactam, the temperature range may be between 70° C. and120° C. The slot die 6 may include a thermocouple and heating cartridgeor other heating component to ensure that the slot die 6 remains withinthe desired temperature range.

While the embodiment herein utilizes a slot die 6 for application of theresin mixture to the fabric or mat 4, the low viscosity of such systemsallows a wide range of application technologies including, but notlimited to, nozzle application, spray application, curtain coating, dipand squeeze coating, kiss roll application, doctor blade application, oreven powder coating of pre-ground solid resins where the curing oven canalso be utilized to melt the reactive components. In other embodiments,the reactive resin may be applied without using an application die. Forexample, a nozzle or other similar application device may be used todeliver the reactive resin to the fabric or mat 4. The nozzle may bemoved laterally across the fabric or mat 4 in delivering the reactiveresin. A nip roller or calendar may then be used to press and squeezethe reactive resin through the fabric or mat 4. The nozzle and rollercombination may be particularly useful in applying thermoplasticpolyurethane (TPU) to a fabric or mat 4. More specifically, due to thehigh reactivity of a reactive TPU resin, a coating die such as a slotdie is not recommended for resin application. The use of a coating dieor slot die in applying a reactive TPU resin may result incuring/polymerization of the reactive resin in the coating die andtherefore the plugging of the die. To apply the reactive TPU resin, anozzle can be mounted onto a cable track or other mechanical mechanismto move the nozzle back and forth across a lateral width of fabric ormat 4. After the application of the reactive TPU resin onto fabric ormat, the compression from nip rollers and/or the double belt mechanismwill squeeze the reactive TPU resin and achieve uniform resindistribution.

The liquid handling lines between the two holding tanks, 1 and 2, andthe mixer 3 and/or between the mixer 3 and the slot die 6 are typicallyinsulated to minimize heat loss as the resin mixtures flow through thehandling lines. In some embodiments, the liquid handling lines areheated in addition to being insulated to ensure that the liquidmaterials (e.g., resins, catalyst, and activator) are maintained withina desired temperature range. Specifically, the liquid transport linesbetween the holding tanks, 1 and 2, (or solitary holding tank) and themixer 3 and/or between the mixer 3 and the slot die 6 are insulated andheated to maintain the liquid materials within a temperature range abovethe melting point of the reactive resin. Controlling the temperature ofthe liquid materials ensures that the resin does not solidify and/orprematurely react within the handling lines.

In the above process, the temperature of the resin is typicallymaintained within a temperature range above the melting point of thereactive resin in order to maintain the resin in a liquid or moltenstate while preventing premature polymerization of the resin prior tothe curing of the material in the oven. The resin components may need tobe recirculated, such as between one or more holding tanks, 1 and 2, andthe mixer 3. Ensuring that the resin is maintained within a desiredtemperature range is important to minimizing or eliminating prematureresin polymerization and/or material build up in the system and/orliquid handling lines.

Of equal importance is the controlling the surrounding environment inthe vicinity of the coated fabric or mat 4 to ensure that the resinmixture is not exposed to ambient moisture. Exposure of the resinmixture to ambient moisture may reduce the conversion of the resin,which may result in a resin to polymer conversion rate of less than 90%.The systems of FIGS. 1A and 1B are designed to isolate the resin mixture(i.e., reactive components) from atmospheric moisture in order toachieve high conversion from monomer/oligomer to polymer. In someembodiments, the entire system may be housed or enclosed in a room orarea in which the environment is controlled to maintain a substantiallymoisture-free environment. Various dehumidification techniques can beused to remove moisture from the ambient air in the room or area.Exemplary dehumidification techniques include desiccantdehumidification, refrigerant dehumidification, and electrostaticdehumidification. In other embodiments, the system may employ a moisturepurge mechanism that is operable to ensure that the humidity in the airsurrounding the coated fabric or mat is substantially zero. In suchembodiments, the moisture purge mechanism need be employed only in thevicinity of the slot die 6 since the fabric or mat 4 is free of theresin material prior to this point. The moisture purge mechanism may bepositioned proximally of the slot die 6 or distally of the slot die 6 asdesired. In either instance, however, the moisture purge mechanismshould be positioned relatively close to the slot die 6 to minimizeexposure of the resin mixture to the surrounding air. For example, thesystem may be enclosed in an area that is purged with a substantiallymoisture-free gas.

In a specific embodiment, the moisture purge mechanism includes anair/gas plenum or tube 7 of FIG. 1A that blows a moisture-free gas ontoone or more surfaces of the coated fabric or mat 4. The air/gas plenumor tube 7 may be positioned atop the fabric or mat 4, or may bepositioned on opposite sides of the fabric or mat as desired. In aspecific embodiment, the air/gas plenum or tube 7 blows dry nitrogenatop or across either or both the top surface or the bottom surface ofthe fabric or mat 4. The air/gas plenum or tube 7 ensure that the areaor vicinity around or adjacent the coated fabric or mat 4 and/or in thevicinity of the curing oven's inlet is kept substantially free ofmoisture. Minimizing the exposure of the resin material to moisture iscritical to ensuring a high conversion rate of the resin material.Accordingly, the use of the drying mechanism (e.g., infrared heater 5)and/or moisture purge mechanism (e.g., air/gas plenum) is important toensuring proper manufacturing of the prepreg. In another specificembodiment, the resin application mechanism as well as the coated fabricor mat may be enclosed in a box 7, as shown in FIG. 1B, that is purgedwith a substantially moisture-free gas.

After the fabric or mat 4 is coated and/or saturated with the resinand/or purge gas is applied to one or more surfaces of the coated fabricor mat 4, the resin impregnated fabric or mat 4 is then passed through acuring oven 8. The temperature of the curing oven 8 is maintained toensure the completion of the polymerization of the resin to athermoplastic polymer. Stated differently, the curing oven 8 ismaintained at a polymerization temperature at which the monomers and/oroligomers start to polymerize. For a reactive resin composition thatincludes caprolactam, the polymerization temperature may be about 120°C. or more (e.g., about 120° C. to about 220°). For prepregmanufacturing processes where the polymerized resin matrix is notmelted, an upper limit on the polymerization temperature for themonomers and/or oligomers may be the melting temperature of the polymer.For example, a reactive resin composition that includes caprolactam mayhave a upper limit of a polymerization temperature that is the meltingtemperature of the PA-6 polymer (i.e., ˜220° C.). The coated fabric ormat 4 may be exposed to the curing oven 8 for a time which is sufficientto ensure complete polymerization of the resin material. For example,for a reactive resin composition that includes caprolactam, theresidence time of the coated fabric or mat in the curing oven may beabout 3 minutes to ensure the complete polymerization of caprolactam.

As noted above, when the reactive resin composition is a combination oftwo or more types of reactive monomers and/or oligomers, the heatingtemperature of the resin-fiber mixture may be chosen to be above athreshold polymerization temperature of one type of monomer/oligomer butbelow a threshold polymerization temperature of the other type ofmonomer/oligomer. For example, a reactive resin composition thatincludes both caprolactam and CBT may be heated to 120-170° C., whichmay polymerize the caprolactam to PA-6 without significantlypolymerizing the CBT to polybutylene terephthalate (PBT). The resultingfiber-resin amalgam will include a polymerized resin matrix of PA-6combined with a polymerizable resin of CBT. The fiber-resin amalgam maybe processed into a reactive prepreg that includes a polymerized resinmatrix of PA-6 and polymerizable CBT. The reactive prepreg may beincorporated into a fiber-reinforced article, where the processingconditions may include polymerizing the CBT into PBT. In otherembodiments, mixtures of monomers and/or oligomers may be used. Forexample, a mixture of caprolactam and laurolactam may be used, whichwill copolymerize in the curing oven to form copolymers with tailoredproperties.

In some embodiments, the coated fabric or mat 4 is subjected to a pressmechanism that facilitates in complete wet-out of the reinforcing fibersby the resin. In one embodiment, the press mechanism may include one ormore calendars that press or squeeze the resin through the fabric or mat4. In another embodiment, the curing oven 8 may be a double beltcompression oven where the pressure on the belts is adjustable tofacilitate complete wet-out of the reinforcing fibers by the resin. Theexposure of the coated fabric or mat to ambient moisture may beminimized by using double belt press that is oil or electrically heated.

Upon exiting the curing oven 8, the fully cured prepreg 9 may becollected. In some embodiments, the system includes a winding mechanismthat is configured to wind the fully cured prepreg 9. In otherembodiments, the fully cured prepreg may be cut into sheets, which maybe stacked atop one another.

The systems of FIGS. 1A and 1B are designed so that the above process isable to be performed in a time of 20 minutes or less, and more commonly10 minutes or less. In some embodiments, the process may be performed in5 minutes or less. Specifically, the time period between when the fabricor mat 4 is initially unwound to when the prepreg exits the curing oven8 may be 20 minutes or less, 10 minutes or less, or in some embodiments5 minutes or less. This speed and impregnation efficiency is notachievable via conventional systems using polymer resin materials.Moreover, the speed and efficiency is not drastically affected whenmultiple stacked layers of the fabric or mat 4 are employed. Rather, thelow viscosity resin mixture is able to easily penetrate through andsaturate the multiple stacked layers of the fabric or mat 4 so that theprocessing time of the stacked layers of the fabric or mat remains low.Full impregnation of the stacked layers of the fabric or mat 4 isachievable due to the low viscosity of the resin materials.

Thermoplastic prepregs, which are sometimes referred to as anorganosheets, offer some superior properties such as impact resistance,thermoformability, and recyclability, as compared to thermoset prepregs.Because of the directionality of fiber orientation in fabrics, however,conventional thermoplastic prepregs have anisotropic mechanicalproperties, which poses significant challenges in designing compositeparts to replace incumbent isotropic materials such as steel andaluminum. In addition, fabric-based thermoplastic prepregs may havelimited conformability, which may increase the difficulty in formingcomposite parts with complex geometry.

As described herein, in some embodiments the thermoplastic prepreg maybe formed of chopped strands or fibers (hereinafter chopped fibers).Specifically, the fiber material in the prepreg may comprise or consistof chopped fibers. The use of chopped fibers in a thermoplastic prepregsmay result in a prepreg with more isotropic mechanical properties andincreased conformability, while maintaining high strength and impactresistance. Such thermoplastic prepregs may be formed in a continuousmanufacturing process that may include: (I) in-line chopping rovingsinto long fibers or strands, which are dispensed uniformly onto a movingbelt to form an un-bonded chopped strand mat; (2) impregnating thechopped fiber or strand mat with a reactive resin such as moltencaprolactam; (3) pressing the coated chopped fiber or strand mat tofully saturate the mat with the reactive resin (e.g., caprolactam); and(4) in-situ polymerizing the reactive resin in an oven to form thechopped fiber or strand thermoplastic prepreg. To ensure the fullpolymerization of the reactive resin, and in particular caprolactam, thefibers or rovings may be in-line dried prior to chopping, and thechopped fiber or strand mat may be further dried prior to theimpregnation with the reactive resin (e.g., caprolactam). The system istypically further configured to maintain a moisture free environment inthe vicinity of the reactive resin coated chopped fiber or strand matprior to subjecting the reactive resin coated chopped fiber or strandmat to the curing oven. Maintaining a moisture free environmentsubstantially prevents exposure of the reactive resin, and in particularcaprolactam, to moisture.

The term chopped fibers relates to fibers that are chopped fromcontinuous rovings or tows. Chopped fibers may have length from 10 mm to100 mm, preferably from 25 mm to 50 mm. The fibers that are employedherein may be selected from, but are not limited to, the following typesof fibers: glass fibers, carbon fibers, basalt fibers, polymer fibersincluding aramid, natural fibers including cellulosic fibers, and otherinorganic fibers. The fibers can be treated with coupling agents, whichmay improve interfacial bonding between fibers and thermoplastic resinmatrix.

The chopped fibers typically form a chopped fiber or strand mat, whichis a fiber mesh or web of unbonded chopped fiber segments. The termun-bonded implies that the mesh or web of chopped fibers is notmechanically or chemically coupled or bonded together, or coupledtogether via some other means. On the other hand, nonwoven matstypically comprise fibers randomly laid atop one another and bonded orcoupled together with an applied binder or adhesive. In otherembodiments, mechanically coupling may be used in place of chemicalcoupling. Mechanically coupling of the fibers may be achieved bymechanical needle punching in which needles or rods are inserted intothe fiber web to encourage or effect entanglement of the fibers. In someinstances, nonwoven mats may include both chemical and mechanicalcoupling of the fibers. Fabrics are mechanically coupled together viathe weaving of the fiber rovings or tows together or stitch bonding.

In contrast to these conventional nonwoven mats, in the instantapplication the web or mesh of chopped fibers is unbonded so thatindividual chopped fibers are not chemically or mechanicallybonded—i.e., a binder or adhesive is not employed nor are mechanicalbonding techniques, such as needle punching. Rather, the chopped fibersare merely laid atop one another with minimal physical engagement. Theresult is that, prior to the addition of the reactive resin, the web ormesh of chopped fibers may be easily separated or pulled apart, such asby the application of a gas over the fiber web or mesh. It should beappreciated that a minimal degree of physically entanglement orengagement will likely be encountered due to the random orientation ofthe chopped fibers in the web or mesh, but that in general the choppedfibers remain uncoupled or unbonded from one another so that the web ormesh has minimal structural integrity prior to application of thereactive resin and the subsequent polymerization to form thermoplasticpolymer.

Once the reactive resin has been added to the chopped fiber web or mesh,the thermoplastic polymer resulted from in-situ polymerization of thereactive resin may function to bond or adhere the chopped fiberstogether. Thus, the thermoplastic polymer functions as the adhesivematrix that bonds or adheres the chopped fibers together. In someembodiments, the chopped fiber web or mesh may be used with a fabric ornonwoven mat, such as those described herein. In such embodiments, thechopped fiber web or mesh may be positioned on a single side or bothsides of the fabric or mat. Because of the very low viscosity of thereactive resin that is commonly employed (e.g., caprolactam), completeimpregnation of the chopped fiber web or mesh is easily achieved in ashort period of time, which ensures a high-volume manufacturing process.Thus, the process described herein has significant advantages in bothproduction efficiency and composite properties, as compared toconventional polymer melt-impregnation processes in which highly viscouspolymeric resin melts are used to impregnate reinforcing fibers.

While the description herein generally refers to the use of an un-bondedchopped fiber web or mesh, it should be appreciated that in someinstances it may be desirable to couple the chopped fibers together viachemical means, mechanical means, or some other means. The reactiveresin may then be added to the coupled or adhered chopped fiber web ormesh. To simplify the description of the various embodiments, thechopped fiber web or mesh will be generally referred to as a choppedfiber web or mesh or more simply a fiber web or mesh. This generaldescription of a chopped fiber web or mesh is meant to describe both anun-bonded or non-adhered chopped fiber web or mesh as well as a bondedor adhered chopped fiber web or mesh. The use of the term in the claimsis likewise meant to cover both the un-bonded/non-adhered chopped fiberweb or mesh as well as the bonded or adhered chopped fiber web or meshunless the claims specifically recite one of these fiber webs or meshes.Thus, the generic description of a chopped fiber web or mesh in thedescription and/or claims may be substituted with the more specificdescription of an un-bonded or non-adhered chopped fiber web or mesh ora bonded or adhered chopped fiber web or mesh if desired.

The resulting chopped fiber thermoplastic prepreg comprises randomlyoriented chopped fibers and possess largely isotropic mechanicalproperties. Due to the excellent conformability of the chopped fibers,the chopped fiber thermoplastic prepreg described herein is capable ofbeing formed into complex-shaped composite parts with deep draws andlarge curvatures, via high throughput processes such as compressionmolding. Additional aspects and features of the chopped fiberthermoplastic prepreg will be appreciated in regards to the descriptionof the various embodiments provided below.

Referring now to FIG. 5, illustrated is a system that may be used toproduce thermoplastic prepregs that include a chopped fiber web or mesh.As described herein, the resulting thermoplastic prepregs are fullyimpregnated with a thermoplastic polymer. The system of FIG. 5 iscapable of producing the fully impregnated thermoplastic prepregs in acontinuous process, in which the chopped fiber web or mesh iscontinually or constantly in movement through the system.

As illustrated in FIG. 5, the system may include two vessels or holdingtanks (i.e., 21 and 22). At least one of the holding tanks functions asa storage and delivery tank of a reactive resin, which is typically amonomer or oligomer that is polymerizable into a thermoplastic polymer.In some embodiments, the monomers or oligomers may include or consist oflactams, lactones, cyclic butylene terephthalate (CBT), methylmethacrylate, precursors of thermoplastic polyurethane, or mixturesthereof. The lactams may include or consist of caprolactam, laurolactam,or mixtures thereof. The holding tanks, 21 and 22, may be heated andpurged with nitrogen to ensure the removal of any moisture, which couldotherwise reduce the reactivity of the raw materials and consequentlyreduce the conversion of the resins to a polymer. As previouslydescribed, one of the holding tanks (e.g., holding tank 21) may containa mixture of a resin and a catalyst. In a specific embodiment, theholding tank (e.g., tank 21) may include caprolactam and a catalyst,such as sodium caprolactamate or any other catalyst. The other holdingtank (e.g., tank 22) may contain a mixture of the resin and anactivator. In a specific embodiment, the other holding tank (e.g., tank22) includes caprolactam and an activator, such as N,N′-hexane-1,6-diylbis(hexahydro-2-oxo-1H-azepine-1-carboxamide) or anyother activator. The holding tanks, 21 and 22, may be heated to atemperature that allows the reactants to melt, such as between about 70and 120° C. for the reactive resin that includes caprolactam. The moltenreactants (e.g., the resin and activator or catalyst) have a very lowviscosity, for example, lower than 10 mPa-s. The viscosity of moltenreactants can be measured according to the test method ISO 3104:1999. Asan example, molten caprolactam at the temperature of 80° C. has aviscosity of 8.5 mPa-s, as measured using ISO 3104:1999.

The reactants from the two holding tanks, 21 and 22, are typicallymetered into a mixer or mixing head 25 that ensures the correct ratio ofthe monomers and/or oligomers, activator, and catalyst is delivered tothe chopped fiber web or mesh. In one embodiment, the mixtures from thetwo holding tanks, 21 and 22, may be provided to the mixer in a 1/1ratio. The mixtures from the two holding tanks, 21 and 22, arethoroughly mixed in the mixer 25 into a substantially homogenousmixture. The mixer 25 may be heated to a temperature that allows thereactants to remain in a liquid non-polymerized state, such as betweenabout 70 and 120° C. for the reactive resin that includes caprolactam.

The system also includes a double belt mechanism that includes an upperbelt 32 and a lower belt 31. The upper belt 32 is positioned atop thelower belt 31 and the two belts are configured to compress or squeeze afiber mesh that is passed through the double belt mechanism. At least aportion of the double belt mechanism is positioned within a curing oven30. In some embodiments, the top belt 32 is fully enclosed within thecuring oven 30. The lower belt 31 has a longitudinal length that issubstantially longer than the upper belt 32 so that at least a portionof the lower belt 31 extends outward from the curing oven 30. Asillustrated, the lower belt 31 may extend outward from a front edge ofthe curing oven 30 by a length L₁, which is typically between 2 and 15feet and more commonly between 3 and 10 feet. In a specific embodiment,the extended length L₁ of the lower belt 31 is between 6 and 9 feet andmore specifically about 8 feet.

The lower belt 31 typically extends outward from the upper belt 32and/or curing oven 30 so that one or more of the components of thesystem may be positioned atop the lower belt 31. For example, a fiberchopper 27 is positioned above the lower belt 31. The fiber chopper 27is configured to cut fiber strands or rovings 26 into chopped fiberstrands C, which form the chopped fiber web or mesh. The fiber chopper27 is positioned above the lower belt 31 so that as the fiber strands orrovings 26 are cut into the individual chopped fiber strands C, thechopped fiber strands C fall atop the lower belt 31 and form the fiberweb or mesh. The fiber strands or rovings 26 may be provided via one ormore spools, 23 a-c, that may be positioned on a creel. The strand orroving that is provided by each spool, 23 a-c, may be similar in fibertype or size or may differ from the strand or roving provided by anotherspool. Thus, the chopped fiber web or mesh may be formed from the sametype of fiber strands or rovings 26 or may be formed from a variety ofdifferent fiber strands or rovings. For example, the chopped fiber webor mesh may include a combination of different sized fibers and/or acombination of different types of fibers. In some instances, two or moredifferent types of fiber strands or rovings, including but not limitedto glass fiber, carbon fiber, and aramid fiber, may be cut by the fiberchopper 27 simultaneously, forming hybrid fiber web or mesh.

In some embodiments, the fibers of the fiber strands or rovings 26 mayinclude a sizing composition having a coupling agent that promotesbonding between the chopped fibers and the thermoplastic polymer. Forexample, the sizing composition may include a coupling activator thatcovalently bonds the polymerization activator moiety to the choppedfibers. In such instances, the bond between the thermoplastic polymerand the chopped fibers may be significantly strengthened or enhanced. Ina specific embodiment, the fiber sizing contains a mixture of silanecoupling agents, polymeric film formers, and other additives that aredesigned to enhance the interfacial bonding between the chopped fibersand a polyamide-6 matrix. Specifically, a reactive silane may be usedthat allows some of the polymerization to be initiated directly from thechopped fiber surface, thus improving the coupling between thereinforcing fibers and the resin matrix to improve composite properties.

In other instances, the activator may be included on the surface of thefibers of the fiber strands or rovings 26 so that the chopped fiber webor mesh includes the activator. In such instances, only a single holdingtank (e.g., tank 21) that contains the resin and catalyst may be used inthe system, or a reduced amount of the activator may be mixed with theresin in the second holding tank (e.g., tank 22). In some embodiments,the two holding tanks, 21 and 22, may each include a different resinmaterial. For example, a first holding tank 21 may include caprolactamwhile the second holding tank 22 includes laurolactam. In suchinstances, a combination of two or more types of reactive monomersand/or oligomers may be applied to the chopped fiber web or mesh.

The system may include a drying mechanism 24 that is configured to drythe fiber strands or rovings 26 as the fiber strands or rovings 26 areunwound from the respective spools, 23 a-c, and before the fiber strandsor rovings 26 are cut via the fiber chopper 27. The drying mechanism 24may be a tubular heater through which the fiber strands or rovings 26are pulled. The system may include a single tubular heater through whichall the fiber strands or rovings 26 are pulled, or may include a tubularheater through which each fiber strand or roving is individually pulledas it is unwound from the respective spool, 23 a-c. The use of thedrying mechanism 24 reduces or eliminates residual moisture that may bepresent on the fiber strands or rovings 26. The drying mechanism 24 mayhave a drying temperature of between 100° C. and 200° C., and morecommonly between 100° C. and 150° C.

The fiber chopper 27 cuts the fiber strands or rovings 26 intoindividual chopped fiber strands C, which fall atop the lower belt 31and form the chopped fiber web or mesh. The individual chopped fiberstrands C are randomly oriented or arranged atop the lower belt 31 andform a fiber web or mesh having a thickness and/or density that dependson the speed of the lower belt 31, the chopping speed of the fiberchopper 27, the number and/or size of fiber strands or rovings 26, andthe like. The chopped fiber web or mesh is typically not subjected tochemical or mechanical bonding and thus, the chopped fiber web or meshis typically un-bonded or un-adhered. Specifically, prior to applicationof the reactive resin, the chopped fiber web or mesh typically does notinclude a binder that bonds or adheres the fiber mesh together and thechopped fiber web or mesh is typically not subjected to a mechanicalentangling process, such as needle punching.

The lower belt 31 carries or conveys the chopped fiber web or meshtoward other components of the system and/or toward an entrance to thecuring oven 30. The chopped fiber web or mesh may be subjected to adrying mechanism 28 that removes residual moisture from the choppedfiber web or mesh. The drying mechanism 28 may be positioned atop thelower belt 31 so that it is above the chopped fiber web or mesh. Thedrying mechanism 28 dries the chopped fiber web or mesh as the choppedfiber web or mesh is moved underneath the drying mechanism 28. Thedrying mechanism 28 may be an infrared heater that raises thetemperature of the chopped fiber web or mesh and thereby removes anyresidual adventitious moisture. One of the reasons for the extendedlength L₁ of the lower belt 31 is to ensure that the chopped fiber webor mesh may be sufficiently dried before the application of the reactiveresin and to ensure that the chopped fiber web or mesh may be subjectedto each of the components of the system. The drying mechanism 28 mayremove trace amounts of surface moisture from the chopped fiber web ormesh.

After the chopped fiber web or mesh is dried via the drying mechanism28, the reactive resin is applied to the chopped fiber web or mesh usinga resin application mechanism 33 that is positioned atop the lower belt31 and above or adjacent the chopped fiber web or mesh. The resinapplication mechanism 33 applies the reactive resin R, which istypically monomers and/or oligomers of the thermoplastic material, tothe chopped fiber web or mesh as the chopped fiber web or mesh is movedpast and typically underneath the resin application mechanism 33. Insome embodiments, the resin application mechanism 33 is a slot diehaving a narrow opening through which the reactive resin R flows, suchas an opening of about 1.0 mm or less. The reactive resin R is deliveredto the resin application mechanism 33 from the mixer 25 via tubing 29,which may be heated to maintain a temperature of the reactive resin.

The reactive resin R may be applied to the chopped fiber web or meshclose to the curing oven 30 in order to minimize exposure of thereactive resin to the surrounding air and environment. In someembodiments, the resin application mechanism 33 may be positioned within10 inches of an inlet of the curing oven and more commonly within 5.0inches or even 1.0 inch of the curing oven's inlet. In otherembodiments, a distal or delivery end of the resin application mechanism33 may be positioned within a hood or cover of the curing oven 30 asillustrated in FIG. 5. The resin application mechanism 33 may betemperature controlled within a desired temperature range, for examplebetween a temperature of 70° C. and 120° C. for the reactive resin thatincludes caprolactam. The resin application mechanism 33 may include athermocouple and heating cartridge or other heating component to ensurethat the resin application mechanism 33 remains within the desiredtemperature range.

As an alternative to the slot die, the resin application mechanism 33may also include a nozzle application, spray application, curtaincoating, dip and squeeze coating, kiss roll application, doctor bladeapplication, or even powder coating of pre-ground solid resins in whichthe curing oven melts the reactive components.

As previously described, the liquid handling lines between the holdingtanks, the mixer, and the resin application die are typically insulatedand/or heated to minimize heat loss as the resin mixtures flow throughthe handling lines. Controlling the temperature of the liquid materialsensures that the resin R does not solidify and/or prematurely reactwithin the handling lines. The temperature of the reactive resin is alsotypically maintained within a desired temperature range in order tomaintain the reactive resin in a liquid or molten state while preventingpremature polymerization of the resin prior to the curing of thematerial in the oven. Similarly, once the chopped fiber web or mesh iscoated with the reactive resin R, the surrounding environment in thevicinity of the coated chopped fiber web or mesh is typically controlledto ensure that the reactive resin is not exposed to ambient moisture inthe environment. Exposure of the reactive resin R to ambient moisturemay reduce the conversion of the reactive resin, which may result in adegree of polymerization less than 90%.

As previously described, the surrounding environment may be controlledby housing or enclosing the system in a room or area in which theenvironment is maintained substantially moisture-free. Variousdehumidification techniques can also be used to remove moisture from theambient air in the room or area. Exemplary dehumidification techniquesinclude desiccant dehumidification, refrigerant dehumidification, andelectrostatic dehumidification. More commonly, the system employs amoisture purge mechanism that is operable to ensure that the humidity inthe air surrounding the coated chopped fiber web or mesh issubstantially zero. For example, the system may employ a moisture purgemechanism that is operable to maintain the relatively humidity in theair surrounding the coated chopped fiber web or mesh to be below 1%.Typically the moisture purge mechanism need only be employed in thevicinity of the resin application mechanism 33 since the chopped fiberweb or mesh is free of the reactive resin R prior to the resinapplication mechanism 33. The moisture purge mechanism may be positionedproximally of the resin application mechanism 33 or distally of theresin application mechanism 33 as desired. In either instance, however,the moisture purge mechanism should be positioned relatively close tothe resin application mechanism 33 to minimize exposure of the reactiveresin to the surrounding air.

As illustrates in FIG. 5, the moisture purge mechanism includes anair/gas plenum or tube 34 that blows a moisture-free gas G onto thechopped fiber web or mesh. The air/gas plenum or tube 34 is positionedatop the lower belt 31 and atop the chopped fiber web or mesh. Theair/gas plenum or tube 34 may be positioned directly adjacent the resinapplication mechanism 33 as illustrated in FIG. 5 so that themoisture-free gas G is blown directly onto the chopped fiber web or meshas the chopped fiber web or mesh is coated with the reactive resin Rfrom the resin application mechanism 33. In a specific embodiment, theair/gas plenum or tube 34 blows dry nitrogen onto the chopped fiber webor mesh. The air/gas plenum or tube 34 ensures that the area or vicinityaround or adjacent the coated chopped fiber web or mesh and/or in thevicinity of the curing oven's inlet is kept substantially free ofmoisture.

After the chopped fiber web or mesh is coated with the reactive resin Rand/or the purge gas G is applied to the coated chopped fiber web ormesh, the coated chopped fiber web or mesh is then subjected to a pressmechanism that facilitates in a complete wet-out of the chopped fibersby the reactive resin. The press mechanism function is typicallyperformed by the upper belt 32 and the lower belt 31, which form adouble belt compression mechanism. As illustrated in FIG. 5, a distalend of the upper belt 32 may be positioned proximally of the curingoven's inlet by a distance L₂, which distance may ensure sufficient roomfor the distal end of the resin application mechanism 33 and air/gasplenum or tube 34 to be positioned within the curing oven 30 between theupper belt 32 and curing oven inlet. The distance L₂ may be between 0.2and 2.0 feet and more commonly between 0.5 and 1.0 feet. The upper belt32 and lower belt 31 compress the coated chopped fiber web or mesh asthe fiber web or mesh is passed through the curing oven 30. Thecompression of the coated chopped fiber web or mesh facilitates in thereactive resin (e.g., monomers and/or oligomers) fully saturating thechopped fiber web or mesh. Fully saturating the chopped fiber web ormesh means that the reactive resin completely impregnates individualchopped fiber strands of the web or mesh. The compression of the coatedchopped fiber web or mesh between the upper belt 32 and lower belt 31also minimizes exposure of the coated chopped fiber web or mesh toambient moisture in the surrounding environment. In some embodiments,the pressing function may be achieved by one or more calendars orrollers that press or squeeze the reactive resin through the choppedfiber web or mesh.

The lower and upper belts, 31 and 32, pass the coated chopped fiber webor mesh through the curing oven 30. The temperature of the curing oven30 is maintained at a temperature that ensures complete polymerizationof the reactive resin. Stated differently, the curing oven 30 ismaintained at a polymerization temperature at which the monomers and/oroligomers start to polymerize, which is typically about 100° C. or more.For a reactive resin composition that includes caprolactam, thepolymerization temperature may be about 120° C. or more (e.g., about120° C. to about 220°). For prepreg manufacturing processes where thepolymerized resin matrix is not melted, an upper limit on thepolymerization temperature for the monomers and/or oligomers may be themelting temperature of the polymer. For example, a reactive resincomposition that includes caprolactam may have a upper limit of apolymerization temperature that is the melting temperature of thepolyamide-6 (i.e., ˜220° C.). The coated chopped fiber web or mesh maybe exposed to the curing oven 30 for a time which is sufficient toensure complete polymerization of the reactive resin material. Forexample, for a reactive resin composition that includes caprolactam, theresidence time of the coated fiber web or mesh in the curing oven may beabout 3 minutes to ensure the complete polymerization of caprolactam.Upon polymerization of the reactive resin, the chopped fiber web or meshis fully impregnated with the thermoplastic polymer. As used herein, thedescription of the chopped fiber web or mesh being fully impregnatedwith the thermoplastic polymer means that the thermoplastic polymerimpregnates the chopped fiber web or mesh to a degree such that thechopped fiber web or mesh has a void content of the composites of lessthan 5% in volume based on the total volume of the thermoplasticprepreg, and more commonly less than 3% in volume based on the totalvolume of the thermoplastic prepreg. In some embodiments, the choppedfiber web or mesh may have a void content of the composites of less than1% in volume based on the total volume of the thermoplastic prepreg.Void content of the resulting prepregs can be measured according to thetest method ASTM D2734-16.

In some instances the system may be configured to ensure that theviscosity of the reactive resin R remains low before the chopped fiberweb or mesh is fully impregnated with the reactive resin. Specifically,the polymerization of the reactive resin R may be controlled to ensurethat the chopped fiber web or mesh is fully saturated with the resinbefore the resin polymerizes.

In some embodiments, a distal end of the oven or enclosure 30 includes acooling mechanism 35 that is configured to cool a fully cured choppedfiber thermoplastic prepreg 36. The cooling mechanism 35 may cool thechopped fiber thermoplastic prepreg 36 in order to allow the choppedfiber thermoplastic prepreg 36 to be cut to shape, to be handled by anindividual, to reduce or prevent warpage of the chopped fiberthermoplastic prepreg 36, or for any other reason. The cooling mechanism35 typically cools the chopped fiber thermoplastic prepreg 36 to below50° C. and more commonly to at or near ambient temperature, which allowsthe chopped fiber thermoplastic prepreg 36 to be handled by anindividual without burning or harming the individual. The coolingmechanism 35 may include chilled water cooling. Upon exiting the curingoven 30, the fully cured chopped fiber thermoplastic prepreg 36 isformed or produced. The system may include a cutting mechanism 38 thatis configured to cut the fully cured chopped fiber thermoplastic prepreg36 into sheets, which may be stacked atop one another. In otherembodiments, the system may include a winding mechanism that isconfigured to wind the fully cured chopped fiber thermoplastic prepreginto a roll product.

The system of FIG. 5 is designed so that the process is performed in atime of 20 minutes or less, and more commonly 10 minutes or less. Insome embodiments, the process may be performed in 5 minutes or less. Thespeed and efficiency of the system is not drastically affected whenmultiple layers of fiber material are employed, such as in the systemsof FIGS. 6-8. Rather, the low viscosity reactive resin is able to easilypenetrate through and saturate the multiple layers of fiber material sothat the overall processing time remains low and relatively unaffected.Full impregnation of the stacked layers is also achievable due to thelow viscosity of the resin materials.

Although the lower belt 31 is illustrated as extending from the inlet ofthe curing oven 30, in some embodiments the lower belt 31 may be fullyenclosed within the curing oven 30, or within a hood or cover of thecuring oven. In such embodiments, the lower belt 31 extends beyond thedistal or front edge of the upper belt 32 so that the other componentsof the system (i.e., the fiber chopper 27, drying mechanism 28, resinapplication mechanism 33, etc.) are able to remain positioned above thelower belt 31. In such an embodiment, the other components of the systemare typically enclosed within curing oven 30, or within a hood or coverof the curing oven 30.

FIG. 6 illustrates a similar system except that the system includesmultiple fiber choppers. Specifically, the system includes a first fiberchopper 27 a and a second fiber chopper 27 b that are each positionedatop the lower belt 31 and configured to cut fiber strands or rovings.The first fiber chopper 27 a cuts first fiber strands or rovings 26 athat are unwound from the respective spools, 23 a-c. The chopped firstfiber strands or rovings 26 a fall atop the lower belt 31 and form afirst layer of a chopped fiber web or mesh. The first strands or rovings26 a may pass through a first roving heater 24 a that dries the firststrands or rovings 26 a. The thickness and/or density of the first layeris controlled by the speed of the first fiber chopped 27 a, the numberand sizes of individual rovings in 26 a, and the speed of the lower belt31. The second fiber chopper 27 b cuts second fiber strands or rovings26 b that are unwound from the respective spools, 23 d-e. The choppedsecond fiber strands or rovings 26 b fall atop the lower belt 31 and/orthe first layer and form a second layer of the chopped fiber web ormesh. The second strands or rovings 26 b may pass through a secondroving heater 24 b that dries the second strands or rovings 26 b. Thethickness and/or density of the second layer is controlled by the speedof the second fiber chopped 27 b, the number and sizes of individualrovings in 26 b, and the speed of the lower belt 31.

The resulting chopped fiber web or mesh may have a layered configurationin which at least one property of the first layer is different than aproperty of the second layer. The properties may differ in fiber type,fiber length, fiber diameter, fiber or layer density, layer thickness,and the like. In some embodiments, the first and second strands orrovings, 26 a and 26 b, may be different fiber types, different fibersizes, and/or have different fiber characteristics. In otherembodiments, the chopped fibers that are produced by the first fiberchopper 27 a and the second fiber chopper 27 b may fall atop the lowerbelt 31 so that a hybrid layer is formed of the chopped fibers. Thehybrid layer may include a mixture of the chopped fibers from the firstand second fiber choppers, 27 a and 27 b. The multiple fiber choppersmay be used simply to cut strands or rovings that have differentproperties. The layered or hybrid chopped fiber web or mesh may then besubjected to the other processes of the system, such as the dryingmechanism 28, resin application mechanism 33, gas purge mechanism 34,double belt compression mechanism, curing oven 30, and the like. In someembodiments, the first and second roving heaters, 24 a and 24 b, may bethe same heater. The system may also include additional fiber choppers(not shown) that cut additional fiber strands or rovings to formadditional layers of the chopped fiber web or mesh as desired.

In some embodiments, the fiber chopper 27 of FIG. 5 may be replaced witha fiber scattering unit (see the fiber scattering unit 37 of FIG. 8A).In such embodiments, the system would look essentially like the systemof FIG. 8A except that the system would not include the roller 41 aboutwhich a fabric or mat 40 is positioned. In such embodiments, the fiberscattering unit 37 would scatter or disperse pre-cut chopped fibersegments C atop the lower belt 31. The pre-cut chopped fiber segments Care typically loaded or positioned within a hopper and accessible to thefiber scattering unit 37. The chopped fiber segments C may be scattereduniformly atop the lower belt 31 to form a chopped fiber web or mesh. Inother embodiments, the first fiber chopper 27 a and/or the second fiberchopper 27 b of FIG. 6 may be replaced with a fiber scattering unit 37to form multiple fiber web or mesh layers and/or to disperse differentfiber sizes or types within the fiber web or mesh. The chopped fibersegments C may be fully dried prior to scattering or dispersing thematop the lower belt 31. The system may include the various othercomponents described herein, or may exclude one or more of the describedcomponents as desired.

FIG. 7 illustrates a hybrid system in which the thermoplastic prepreg isformed of both the chopped fiber web or mesh and a fabric or mat. Thesystem includes a roller 41 about which a fabric or mat 40 ispositioned. The system is configured to unwind the fabric or mat 40 fromthe roller and to move the fabric or mat 40 atop the lower belt 31. Thefiber chopper 27 is positioned above the lower belt 31 and the fabric ormat 40 so that the chopped fibers C fall atop the fabric or mat 40 andtypically form a chopped fiber web or mesh layer atop the fabric or mat40. The thickness of the chopped fiber web or mesh may be controlled bycontrolling a speed of the fiber chopped 27, and/or a speed of the lowerbelt 31. In some embodiments the fiber chopper 27 may be replaced with afiber scattering unit. In some embodiments, the fabric or mat 40 may bereplaced with a unidirectional tape that is pre-impregnated with athermoplastic resin.

In some embodiments the chopped fibers C may fall within the fabric ormat 40 to form a hybrid layer that consists of the fabric or mat 40 andthe chopped fiber web or mesh. In such embodiments, the fabric or mat 40must be porous enough to enable the chopped fibers C to fall within andthrough the fabric or mat 40. The fibers or strands 26 may be cut insufficient small pieces to facilitate dispersion of the chopped fibers Cwithin the fabric or mat 40.

The resulting layered or hybrid mat is then moved past the dryingmechanism 28 to remove residual moisture from the layered or hybrid mat.The layered or hybrid mat is then moved past the resin applicationmechanism 33 so that the reactive resin is applied to the mat and ismoved past the gas purge mechanism 34 so that the moisture free gas G isapplied to the layered or hybrid mat. The layered or hybrid mat is thenmoved through the double belt mechanism to fully saturate the layered orhybrid mat and moved through the curing oven 30 to polymerize thereactive resin. Upon polymerization of the reactive resin, thethermoplastic polymer fully impregnates the layered or hybrid mat.

The layered or hybrid mat may provide several advantages overthermoplastic prepregs that employ only a fabric or mat. In particular,the layered or hybrid mat may have improved conformability. The improvedconformability of the thermoplastic prepreg allows the prepreg to moreeasily conform to molds having complex shapes. Thus, it is easier toform the prepreg into complex shapes. The use of the fabric or mattypically provides improved strength over prepregs that merely employchopped fiber webs or meshes.

FIG. 8 illustrates another hybrid system in which multiple fiberchoppers and a single fabric or mat is employed. It should be realizedthat the configuration of the system of FIG. 8 may be reversed so thatmultiple fabrics or mats and a single fiber chopper is employed.Alternatively, the system of FIG. 8 may use both multiple fabrics ormats and multiple fiber choppers if desired to form a thermoplasticprepreg having a desired chopped fiber web or mesh and fabric or matconfiguration.

In FIG. 8, a first fiber chopper 27 a is positioned atop a distal end ofthe lower belt 31. The first fiber chopper 27 a cuts first fiber strandsor rovings 26 a that are unwound from about respective spools, 23 a-c.The chopped first fiber strands or rovings 26 a fall atop the lower belt31 and form a first layer of a chopped fiber web or mesh. The firststrands or rovings 26 a may pass through a first roving heater 24 a thatdries the first strands or rovings 26 a. The thickness and/or density ofthe first layer is controlled by the speed of the first fiber chopped 27a, the number and sizes of individual rovings in 26 a, and the speed ofthe lower belt 31. The system also includes a roller 41 about which afabric or mat 40 is positioned. The fabric or mat 40 is unwound from theroller 41 and is moved atop the chopped fiber web or mesh formed by thefirst chopped fiber strands or rovings 26 a. A guiding roller 42 may bepositioned above the lower belt 31 to properly direct the fabric or mat40 onto and atop the chopped fiber web or mesh. A second fiber chopper27 b is positioned proximally of the fabric or mat roller 41 and isconfigured to cuts second fiber strands or rovings 26 b that are unwoundfrom about respective spools, 23 d-f. The chopped second fiber strandsor rovings 26 b fall atop the fabric or mat 40 and form a second layerof the chopped fiber web or mesh atop the fabric or mat 40. The secondstrands or rovings 26 b may pass through a second roving heater 24 bthat dries the second strands or rovings 26 b. The thickness and/ordensity of the second layer is controlled by the speed of the secondfiber chopped 27 b, the number and sizes of individual rovings in 26 b,and the speed of the lower belt 31. The fabric or mat 40 is thussandwiched between two layers of chopped fiber webs or meshes. Thefabric or mat and chopped fiber webs or meshes are then moved throughthe system to remove residual moisture, apply the reactive resin, andpolymerize the reactive resin. The resulting hybrid thermoplasticprepreg 36 may then be cut into sheets via a cutting mechanism 38 asdescribed herein.

FIG. 8A illustrates a hybrid system in which the fiber chopper isreplaced with a fiber scattering unit 37. The fiber scattering unit 37is configured to scatter or disperse pre-cut chopped fiber segments Cthat are loaded or positioned within a hopper. In some embodiments, thechopped fiber segments C are scattered uniformly atop the lower belt 31to form a chopped fiber web or mesh. In such embodiments, the system ofFIG. 8A does not include the roller 41 and fabric or mat 40. In otherembodiments, the chopped fiber segments C are uniformly scattered atop afabric or mat 40 to form a layer of the chopped fiber web or mesh atopthe fabric or mat 40. In some embodiments, the fabric or mat 40 may bereplaced with a unidirectional tape that is pre-impregnated with athermoplastic resin. The system of FIG. 8A may include an additionalfiber scattering unit 37 and/or fiber chopper to form additional fiberweb or mesh layers and/or to disperse different fiber sizes or typeswithin the fiber web or mesh. The chopped fibers C may be fully driedprior to scattering or dispersing them atop the lower belt 31 or fabricor mat 40. The system may include the various other components describedherein, or may exclude one or more of those components as desired.

FIG. 8B illustrates a hybrid system in which the fully cured choppedfiber thermoplastic prepreg 36 is wound into a roll product via awinding mechanism 39. The thermoplastic prepreg may be formed solely ofa chopped fiber web or mesh or may be formed of both the chopped fiberweb or mesh and a fabric or mat. When the thermoplastic prepreg isformed of the chopped fiber web or mesh and fabric or mat, the systemincludes a roller 41 about which a fabric or mat 40 is positioned aspreviously described. The system of FIG. 8B may include one or morefiber choppers and/or rollers 41 to form any type of layered prepregthat is desired.

Referring now to FIG. 15, illustrates a system that uses an alternativemeans of delivering the reactive resin R to the resin applicationmechanism 33. In a specific embodiment, the holding tank, or holdingtanks (i.e., tanks 21 and 22), are replaced by an extruder 102 that isconfigured to deliver the molten reactive resin R to the resinapplication mechanism 33. Since the reactive resin R is delivereddirectly to the resin application mechanism 33, the mixer 25 is alsotypically removed from the system, although in some embodiments, thesystem may employ a mixer 25 along with the extruder 102. A distal endof the extruder 102 may be directly coupled with the resin applicationmechanism 33 or a hose 120, or other connection, may couple the extruder120 to the resin application mechanism 33. The reactive resin R may befed from the extruder 102 through the hose 120 to the resin applicationmechanism 33. The feed rate of the reactive resin R to the resinapplication mechanism 33 is generally based on the throughput of thesystem.

One or more hoppers or feeders (not shown) are typically attached to theextruder 102 via one or more delivery ports. The hopper or feederdelivers raw materials (e.g., monomer, oligomer, activator, catalyst,and the like) to the extruder 102. The hopper or feeder is typicallydesigned to deliver the raw materials at a constant rate. The extruder102 is commonly a twin-screw extrusion device. The extruder 102 isdesigned to heat up the raw materials to melt the materials within theextruder 102. The extruder 102 is also configured to mix the melted rawmaterials. As such, the extruder 102 functions in a manner similar tothe mixer 25. The extruder 102 is typically heated to above a meltingpoint of the raw materials while being maintained at a temperature atwhich polymerization is minimized or prevented. For example, when themonomer includes or consists of caprolactam, the extruder 102 may beheated to between 70-120 degrees Celsius. Because of the very lowviscosity of molten caprolactam, the screw elements in the extruder 102may be designed to effectively melt and mix caprolactam with catalystand activator.

The system may include the various other components described herein, ormay exclude one or more of those components as desired. For example, inFIG. 15, the system includes a roller 41 about which a fabric or mat 40is rolled. The fabric or mat 40 is unrolled from the roller 41 atop alower belt 31 of the system. The fabric or mat 40 is then subjected tothe various processes described herein. The reactive resin R is appliedto the fabric or mat 40 from the resin application mechanism 33. Thereactive resin R is delivered to the resin application mechanism 33 fromthe extruder 102 in a low viscosity liquid state as described herein.The low viscosity reactive resin R ensures that the reactive resin Rfully saturates and impregnates the fabric or mat 40 as describedherein. The extruder 102 is configured to minimize or preventpolymerization of the reactive resin R to ensure that the reactive resinR is delivered to the resin application mechanism 33 in a low viscosityand unpolymerized state.

FIG. 16 illustrates another system in which the holding tank(s) arereplaced by an extruder 102 that mixes and delivers the reactive resin Rto the resin application mechanism 33. The system of FIG. 16 includes anapplication mechanism 110 that applies a material M atop the lower belt31 of the system. The application mechanism 110 may be configured toapply various materials atop the lower belt 31. In some embodiments, theapplication mechanism 110 may replace the roller 41 and the fabric ormat 40. In other embodiments, the application mechanism 110 may be usedin addition to the fabric or mat 40. In such embodiments, the system ofFIG. 16 would be modified to include a roller 41 or other component thatis designed to position the fabric or mat 40 atop the lower belt 31. Theapplication mechanism 110 may include one or more mechanisms including afiber scattering unit, a fiber chopper, and/or a powder applicator. Insuch embodiments, the material M that is applied atop the lower belt 31,or the fabric or mat 40, may include chopped fibers, a lightweightmaterial, a filler material, and the like. The lightweight fillermaterial may include hollow glass microspheres, perlite, or anothermaterial. The application of a lightweight filler material is furtherdescribed in U.S. application Ser. No. 16/172,153, filed Oct. 26, 2018,and entitled “System for Producing a Fully Impregnated ThermoplasticPrepreg”, the entire disclosure of which is incorporated by referenceherein. The chopped fibers may include glass fibers, polymer fibers,and/or any other type of fiber described herein. The lightweight fillermaterial may be applied to increase a thickness of the final productand/or to decrease a density of the final product. The chopped fibersmay form a fiber web or mesh atop the lower belt 31 as described herein.While FIGS. 15 and 16 illustrate two specific systems that employ anextruder 102, it should be realized that the disclosure is not limitedto these systems and that an extruder 102 may be used in any of thesystems described or incorporated herein, and/or that variousmodifications may be made to any of the systems so that the systems areable to form a desired thermoplastic prepreg.

FIGS. 17-20 illustrate various embodiments of extruders 102 that may beused to deliver the reactive resin R to the resin application mechanism33. Referring now to FIG. 17, the extruder 102 includes a proximal end104 and a distal end 106. The distal end 106 of the extruder 102 isfluidly coupled to the resin application mechanism 33 in order todeliver the liquid reactive resin R to the resin application mechanism33. In some embodiments, the distal end 106 of the extruder 102 iscoupled with a hose (not shown) that fluidly couples with the resinapplication mechanism 33 or the distal end 106 of the extruder 102 isdirectly coupled with the resin application mechanism 33. The extruder102 includes a first screw 101 and a second screw 103 that are housedwithin a body of the extruder 102 and that are configured to melt andmix the raw materials together. The extruder 102 includes a materialport 108 through which the raw materials are delivered. The rawmaterials (not shown) are typically fed into the material port 108 inpellet or powder form. The raw materials include or consist of 1) amonomer, oligomer, or monomer/oligomer combination; 2) a catalyst;and/or 3) an activator. The monomers and/or oligomers may include orconsist of any of the materials described herein, and any equivalentsthereof. Similarly, the activator and catalyst may include or consist ofany of the materials described herein, and any equivalents thereof. Theraw materials may be added in various amounts. In a specific embodimentthe amount of the activator and catalyst may be between 0.5 and 5.0% byweight of the monomer.

The twin-screws, 101 and 103, of the extruder 102 are typically heatedto a temperature above a melting temperature of the monomer or oligomer.In this manner, the twin-screws, 101 and 103, facilitate or effectmelting of the monomer, oligomer, activator, and/or catalyst. Thetwin-screws, 101 and 103, actively mix the materials so that ahomogenous or uniform reactive resin R mixture is formed or achievedprior to the distal end 106 of the extruder 102. The extruder 102 ofFIG. 17 includes a single material port 108 into which the raw materialsare fed. As such, a longitudinal length of the extruder 102 is typicallyshort in order to minimize or prevent premature polymerization of thereactive resin R. Specifically, as described herein, the reactive resinmay be a material that quickly polymerizes upon heating and mixing withthe catalyst and activator. As such, introducing all the materialstogether via a single material port 108 may increase the chance ofpremature polymerization. To minimize an occurrence of prematurepolymerization, the extruder 102 may be maintained at a temperatureclose to the melting temperature of the monomer and/or oligomer, and/orthe length of the extruder 102 may be relatively short so that thereactive resin R is quickly extruded or delivered to the resinapplication mechanism 33.

FIG. 18 illustrates an extruder 102 that is designed to further minimizepremature polymerization of the monomer and/or oligomer. The extruder102 of FIG. 18 includes a pair of material ports that are located atdifferent positions along the longitudinal length of the extruder 102.The monomer and/or oligomer raw materials may be fed into a firstmaterial port 108 along with either the activator or catalyst. Thematerial that is not fed into the first material port 108 (i.e., theactivator or catalyst) is fed into a second material port 105. Forexample, if the activator is fed into the first material port 108, thecatalyst is fed into the second material port 105, or vice versa. Themonomer and/or oligomer may also be fed into the second material port105 along with the activator or catalyst. In this manner, the rawmaterials are not all fed simultaneously into the extruder 102 via asingle material port, which greatly minimizes premature polymerizationof the reactive resin R. The twin-screws, 101 and 103, melt and mix theraw materials (e.g., monomer, oligomer, and/or activator) that are fedinto the first material port 108 as the materials are transportedbetween the first material port 108 and the second material port 105.The twin-screws, 101 and 103, then melt and mix the raw materials (e.g.,monomer, oligomer, and/or catalyst) that are fed into the secondmaterial port 105. The materials continue to mix until they aredelivered or extruded from the distal end 106 of the extruder 102 to theresin application mechanism 33. It should be realized that the materialsmay be fed into the first material port 108 and second material port 105in any combination.

FIG. 19 illustrates another extruder 102 that is designed to minimizepremature polymerization of the monomer and/or oligomer. The extruder102 of FIG. 19 includes three material ports that are located atdifferent positions along the longitudinal length of the extruder 102.In the extruder of FIG. 19, the materials may be fed separately into theextruder 102, which greatly reduces premature polymerization of themonomer and/or oligomer. For example, the monomer and/or oligomer rawmaterials may be fed into a first material port 108, while the activatorraw materials are fed into a second material port 105, and the catalystraw materials are fed into a third material port 107. The raw materialsthat are fed into each material port may be varied as desired and/or anycombination of the raw materials may be fed into any of the materialports. The twin-screws, 101 and 103, melt and mix each of the materialsthat are fed into the respective ports as the materials are transportedbetween the ports. The twin-screws, 101 and 103, continue to mix thematerials until they are delivered or extruded from the distal end 106of the extruder 102 to the resin application mechanism 33.

FIG. 20 illustrates another extruder 102 that is designed to minimizepremature polymerization of the monomer and/or oligomer. In addition tothe components illustrated in FIG. 17, the extruder 102 of FIG. 20includes a distally positioned extruder 109 that is configured todeliver one or more of the raw materials into the extruder 102. Theextruder 109 commonly includes a single screw 111 that delivers orextrudes the material into the extruder 102. In other embodiments, thesingle screw 111 may be replaced with twin-screws or any other extrusionmechanism.

The extruder 109 is positioned at the distal end of the extruder 102 sothat the raw materials are delivered into the distal end of the extruder102. Since the materials are delivered into the distal end of theextruder, the materials are mixed at the distal end of the extruder 102with the materials that are fed into the material port 108 immediatelybefore the reactive resin R is delivered or extruded into the resinapplication mechanism 33. Premature polymerization is greatly minimizedor prevented since all the materials are not combined until the distalend of the extruder 109. The materials that are delivered via theextruder 109 typically include or consist of the catalyst or theactivator, although any combination of the monomer, oligomer, activator,catalyst, or a filler material may be delivered through the extruder109. The extruder 109 is configured to heat and melt the raw materialpowder or pellets that is fed into the extruder 109. As such, theextruder 109 delivers a liquid material to the distal end of theextruder 102, which is easily mixable with the materials fed through thematerial port 108 since the material does not need to be melted. Ifmultiple materials are fed into the extruder 109, the extruder 109 mixesthe materials in addition to melting the materials. In some embodiments,a mixer may be used between the distal end of the extruder 102 and theresin application mechanism 33.

Exemplary Prepreqs

The above system may be used to manufacture a fully impregnatedthermoplastic prepreg. The thermoplastic prepreg may include a fabric ormat, a chopped fiber web or mesh, or a hybrid web or mat. In oneembodiment, the fabric or mat may include a plurality of rovings thatare woven together. Each roving may contain a bundle of continuous glassfibers or any other fibers. In another embodiment, the fabric or mat mayinclude a plurality of entangled and intermeshed fibers that arerandomly oriented. In yet another embodiment, a web or mesh of un-bondedchopped fibers may be employed. The prepreg also includes athermoplastic polymer that is fully impregnated within the fabric ormat, a chopped fiber web or mesh, or a hybrid web or mat. Thethermoplastic polymer is formed by polymerizing a reactive resin (e.g.,caprolactam, CBT, and the like) to form the thermoplastic polymer (e.g.,polyamide-6, PBT, and the like). As described herein, greater than 90%,95%, 98%, or even 99% by weight of the resin reacts to form thethermoplastic polymer. When the fully impregnated thermoplastic prepregis subjected to a subsequent heating and/or pressure process, thethermoplastic polymer melts or softens to allow the thermoplasticprepreg to be molded or formed into a composite part.

In some embodiments, the fully impregnated thermoplastic prepreg is arolled product. In some other embodiments, the fully impregnatedthermoplastic prepreg may be cut to sheets. The thermoplastic prepregmay be subsequently formed into a composite part. For example, one ormore layers of the thermoplastic prepreg may be compression molded intoa desired composite part. Exemplary techniques for forming the prepregsinto the fiber-reinforced composite articles may include compressionmolding of a single prepreg layer, multiple prepreg layers, and/orpellets of prepreg material into the fiber-reinforced article. When theprepreg includes partially-polymerized resin, the compression moldingprocess may include a heating step (e.g., hot pressing) to fullypolymerize the resin. Heat may also be used in the compression moldingof fully-polymerized prepregs to melt and mold the prepreg into theshape of the final article.

The prepregs may also be used to in conjunction with other fibers andresin materials to make the final composite article. For example, theprepreg may be placed in selected sections of a tool or mold toreinforce the article and/or provide material in places that aredifficult to reach for thermoset and/or thermoplastic resins. Forexample, the prepregs may be applied to sharp corners and other highlystructured areas of a mold or layup used in reactive injection moldingprocesses (RIM), structural reactive injective molding processes (SRIM),resin transfer molding processes (RTM), vacuum-assisted resin transfermolding processes (VARTM), spray-up forming processes, filament windingprocesses, and long-fiber injection molding processes, among others. Theprepreg may also be used as local reinforcement or for overmoldingduring injection and compression molding processes including LFT (longfiber thermoplastic) and D-LFT (direct-long fiber thermoplastic).

Exemplary composite products that may be formed from the prepregsinclude: automotive components, wind turbine blade components, buildingand construction components, electrical components, sports and leisurecomponents, and/or other components. Exemplary automotive componentsinclude: cockpit, seats, instrument panels, side beams, bottom plate,bottom plate side beam, door trims, body panels, openings, underbody,front/rear modules, engine compartment, engine covers, battery trays,oil pans, bonnets/hoods, fenders, spoilers, and the like.

Exemplary wind turbine blade components include: spar cap, shells, rootinserts, and the like. Exemplary building and construction componentsinclude: columns, pediments, domes, panels, window profiles, ladderrails, and the like. Exemplary electrical components include: lightpoles, circuit boards, electrical junction boxes, and the like.Exemplary sports and leisure components include: golf club shafts, golftrolleys, and the like. Other components that may be formed form theprepregs include: components for mass transportation, agriculturalequipment, and trailers/RV including passenger seats, standbacks, wallcladdings, floor panels, large panels for trailer walls, truck andtractor cabs, bus body shells, cargo containers, and the like.

In a specific embodiment, a battery tray or compartment for an electriccar or vehicle may be molded using the fully impregnated thermoplasticprepregs described herein. The battery compartment may be molded from asingle piece of the prepreg material, thereby eliminating the need touse unidirectional tape on the corners or edges to reinforce these areasof the battery compartment, as is done in conventional processes.

Referring to FIG. 9, illustrated is a thermoplastic prepreg that may beformed by one of the systems and/or methods described herein. Thethermoplastic prepreg includes a web or mesh of fibers 50 that includesa plurality of chopped fibers 51 having a fiber length and a fiberdiameter. The fiber length is typically between 10 and 100 mm and morecommonly between 25 and 50 mm. The fiber diameter is typically between 1and 30 μm and more commonly between 5 and 20 μm. As described herein,the web or mesh of fibers 50 is typically un-bonded prior to theapplication of a reactive resin and thus, the web or mesh of fibers 50is typically not mechanically bonded and does not include a binder otherthan the thermoplastic material that binds the chopped fibers together.The web or mesh of fibers 50 is also not typically coupled together viasome means other than the thermoplastic material. The web or mesh offibers 50 may include multiple fiber types and/or fiber sizes asdescribed herein that are homogenously or uniformly dispersed within theweb or mesh of fibers 50 and that form a hybrid fiber mesh. The choppedfibers 51 may include a sizing composition that has a coupling agentthat promotes bonding between the chopped fibers 51 and thethermoplastic polymer. The chopped fibers may include or consist ofglass fibers, carbon fibers, basalt fibers, metal fibers, ceramic fiber,natural fibers, synthetic organic fibers, aramid fibers, inorganicfibers, or combinations thereof. In some instances, it may be beneficialto use a chemically or mechanically coupled web or mesh of fibers 50 andthus, the web or mesh of fibers 50 is not limited to a specificconfiguration (i.e., bonded or un-bonded) unless specifically recited inthe claims.

The thermoplastic material fully impregnates the web or mesh of fibers50 so that the thermoplastic prepreg has a void content of less than 5%and more commonly less than 3%. In most embodiments, the thermoplasticprepreg has a void content of less than 3% and sometimes less than 1%.As described herein, the thermoplastic material comprises or consists ofpolymers that are formed by in-situ polymerization of monomers oroligomers in which greater than 90%, 95%, 98%, or even 99% by weight ofthe monomers or oligomers react to form the thermoplastic material. Thethermoplastic prepreg includes 5 to 95 weight percent of thethermoplastic material. The thermoplastic material may include orconsist of nylon, PMMA, PBT, thermoplastic polyurethane (TPU), ormixtures thereof.

FIG. 10 illustrates another thermoplastic prepreg in which the web ormesh of fibers includes a first layer 50 a of fibers formed of firstchopped fibers 51 a and a second layer 50 b of fibers formed of secondchopped fibers 51 b. The first chopped fibers 51 a and second choppedfibers 51 b are typically different fiber types and/or fiber sizes. Thecomposition of each fiber layer, the density of each fiber layer, and/orthe thickness of each fiber layer may be selected based on a givenapplication for the thermoplastic prepreg and/or based on a desiredprepreg property. The first chopped fibers 51 a and second choppedfibers 51 b are typically not entangled or intermixed except for at aninterface between the first layer 50 a and the second layer 50 b. Thethermoplastic material fully impregnates the webs or meshes of fibers.The thermoplastic prepreg may have a void content and polymerizationpercentage as described herein. The thermoplastic prepreg of FIG. 10 maybe formed via the system illustrated in FIG. 6.

FIG. 11 illustrates a thermoplastic prepreg that has a layeredconfiguration in which each layer includes a different fiberreinforcement. Specifically, a first layer of the thermoplastic prepregincludes the web or mesh of chopped fibers 50 and a second layer of thethermoplastic prepreg includes a fabric or mat 52. As described hereinthe fabric or mat 52 is typically formed of continuous fiber strands ora plurality of entangled or bonded fiber segments. In some embodiments,the second layer of the thermoplastic prepreg that includes a fabric ormat 52 may be replaced with a unidirectional tape. The composition ofeach layer, the density of each layer, and/or the thickness of eachlayer may be selected based on a given application for the thermoplasticprepreg and/or based on a desired prepreg property. The thermoplasticmaterial fully impregnates the fiber reinforcement. The thermoplasticprepreg may have a void content and polymerization percentage asdescribed herein. The thermoplastic prepreg of FIG. 11 may be formed viathe system illustrated in FIG. 7.

FIG. 12 illustrates a thermoplastic prepreg that has a layeredconfiguration in which the fabric or mat 52 is sandwiched between anupper layer of the web or mesh of chopped fibers 50 and a lower layer ofa web or mesh of chopped fibers 53. The composition of each layer, thedensity of each layer, and/or the thickness of each layer may beselected based on a given application for the thermoplastic prepregand/or based on a desired prepreg property. The thermoplastic materialfully impregnates the fiber reinforcement. The thermoplastic prepreg mayhave a void content and polymerization percentage as described herein.The thermoplastic prepreg of FIG. 12 may be formed via the systemillustrated in FIG. 8.

FIG. 13 illustrates a thermoplastic prepreg that also has a layeredconfiguration, but is opposite the configuration of FIG. 12 in that theweb or mesh of chopped fibers 50 is sandwiched between an upper layer ofthe fabric or mat 52 and a lower layer of a fabric or mat 54. Thecomposition of each layer, the density of each layer, and/or thethickness of each layer may be selected based on a given application forthe thermoplastic prepreg and/or based on a desired prepreg property.The thermoplastic material fully impregnates the fiber reinforcement.The thermoplastic prepreg may have a void content and polymerizationpercentage as described herein. The thermoplastic prepreg of FIG. 13 maybe formed via a system similar to that illustrated in FIG. 8 in which asingle fiber chopper is employed and two fabrics or mats are employed.Alternatively, thermoplastic prepregs formed via the system of FIG. 1Aor 1B may be laminated with a thermoplastic prepreg formed via any ofthe systems of FIGS. 5-7. In some embodiments, the lower layer of afabric or mat 54 may be replaced with a unidirectional tape. In suchembodiments, the web or mesh of chopped fibers 50 may be sandwichedbetween an upper layer of the fabric or mat 52 and a lower layer ofunidirectional tape.

In some embodiments, the thermoplastic prepregs described herein may notbe fully polymerized. As such, the thermoplastic prepregs may include aresidual resin content—e.g., a residual monomer or oligomer content. Theresidual resin content consists of monomers or oligomers that have notpolymerized into the thermoplastic material. For example, thethermoplastic material of a thermoplastic prepreg may include between0.5 and 5 percent of the residual monomers or oligomers, and morecommonly between 1 and 3 percent, or between 1 and 2 percent, of theresidual monomers or oligomers. The percentage of residual monomers oroligomers that is present in the thermoplastic material is determined inrelation to the amount of resin that was initially added to the fiberreinforcement. For example, a residual monomer or oligomer content ofbetween 0.5 and 5 percent means that 0.5-5 percent of the resin that wasadded to the fiber reinforcement remains in the unpolymerized state. Thecontent of residual monomer or oligomer in the prepreg can be measuredvia a solvent extraction method as descried herein below. For example,the amount of residual caprolactam in polyamide-6 prepreg can bemeasured via the extraction of grounded powder of prepreg using hotwater. The thermoplastic material of the thermoplastic prepreg may havea higher molecular weight than conventional thermoplastic prepregs. Forexample, the thermoplastic prepreg may include a higher molecular weightpolyamide-6 material. In such embodiments, the higher molecular weightthermoplastic material may be evidenced by a non-solubility of thepolyamide-6 material in a solvent in which conventional hydrolyticallypolymerized polyamide-6 resin is typically soluble. For example,polyamide-6 resin formed via in situ anionic polymerization ofcaprolactam may be insoluble in solvents such as hexafluoroisopropanol(HFIP), while the common hydrolytically polymerized polyamide-6 issoluble in HFIP.

The thermoplastic prepregs of FIGS. 9-13 may be roll products or may becut into individual segments as desired. In one embodiment, thethermoplastic prepregs may comprise 30 to 80% by weight of fibrousmaterial and 20 to 70% by weight of thermoplastic polymer. In anotherembodiment, the thermoplastic prepreg may comprise 50 to 70% by weightof fibrous material and 30 to 50% by weight of thermoplastic polymer.

Methods of Forming a Thermoplastic Prepreg Product

FIG. 2 illustrates a method 200 of forming a fully impregnatedthermoplastic prepreg product. At block 210 a fabric or mat is movedfrom a starting point to an ending point. The fabric or mat is subjectedto a plurality of processes between the starting point and ending pointand is in substantially constant movement between the starting point andending point. At block 220, the fabric or mat is dried to removeresidual moisture from one or more surfaces of the fabric or mat. Atblock 230, a monomer or oligomer is mixed with a catalyst and anactivator to form a reactive resin mixture. The catalyst and activatorfacilitate in polymerizing the monomer or oligomer to form athermoplastic polymer. In some embodiments, a portion of the monomer oroligomer may be mixed with the catalyst in a first tank and a portion ofthe monomer or oligomer may be mixed with the activator in a second tankthat is separate from the first tank. In such embodiments, mixing themonomer or oligomer with the catalyst and the activator comprises mixingthe materials from the first tank and the second tank in a mixer.

At block 240, the reactive resin mixture is applied to the fabric ormat. The reactive resin mixture may have a viscosity of lower than 10mPa-s. At block 250, the reactive resin mixture coated fabric or mat ispassed through a calendar or press that presses the reactive resinmixture through the fabric or mat so that the reactive resin mixturefully saturates the fabric or mat. At block 260, the reactive resinmixture coated fabric or mat is passed or moved through a curing oven topolymerize the reactive resin mixture and thereby form the thermoplasticpolymer. During at least a portion of the above process, an environmentin the vicinity of the coated fabric or mat is controlled to maintain ahumidity in the air to substantially zero. Greater than 90%, 95%, 98%,or even 99% by weight of the reactive resin mixture may be reacted toform the thermoplastic polymer.

In some embodiments, the method may also include applying amoisture-free gas to one or more surfaces of the reactive resin mixturecoated fabric or mat to control the environment in the vicinity of thefabric or mat. In a specific embodiment, nitrogen gas may be applied tothe one or more surfaces of the reactive resin mixture coated fabric ormat. In some embodiments, the method may further include winding thecured thermoplastic prepreg into a roll product. In some embodiments,the curing oven may be a double belt compression oven. In suchembodiments, block 250 and 260 may occur simultaneously.

FIG. 3 illustrates another method 300 of forming a fully impregnatedthermoplastic prepreg product. At block 310, a reactive resin is appliedto a fabric or mat, the resin being combined with a catalyst and anactivator that facilitate in polymerizing the resin to form athermoplastic polymer. The catalyst and activator may be housed inseparate holding tanks with or without the resin and may be mixedtogether with the resin prior to application of the resin to the fabricor mat. Alternatively, the catalyst or the activator may be pre-appliedto the fibers of the fabric or mat and the other material may be appliedto the fabric or mat with the resin. At block 320, the resin coatedfabric or mat is passed or moved through a calendar or press to fullysaturate the fabric or mat with the resin. At block 330, the resincoated fabric or mat is passed or moved through a curing oven topolymerize the resin and thereby form the thermoplastic polymer. Stateddifferently, the resin coated fabric or mat is passed or moved throughthe oven to polymerize the resin and thereby form the polymer. During atleast a portion of the above process, humidity in the vicinity of thecoated fabric or mat is maintained at substantially zero. In addition,the above process occurs in a time of 20 minutes or less, 10 minutes orless, or 5 minutes or less.

In some embodiments, the method further includes drying the fabric ormat prior to application of the resin to remove residual moisture fromone or more surfaces of the fabric or mat. In such embodiments, aninfrared heater, pre-drying oven, or other drying device may be used toremove residual moisture from the fabric or mat.

In some embodiments, the method further includes applying amoisture-free gas to one or more surfaces of the fabric or mat tomaintain the humidity in the vicinity of the fabric or mat tosubstantially zero. In such embodiments, nitrogen gas may be blownacross or onto one or more surfaces of the coated fabric or mat. In someembodiments, the method additionally includes winding the fullyimpregnated thermoplastic prepreg into a roll product. In some otherembodiments, the method additionally includes cutting the fullyimpregnated thermoplastic prepreg into sheets.

FIG. 14 illustrates a method 400 of forming a thermoplastic prepregproduct. At block 410, a fiber mesh is moved atop a lower belt of adouble belt press mechanism. The fiber mesh includes chopped fibers. Atblock 420, the fiber mesh is dried via a drying mechanism that ispositioned atop the lower belt and that is configured to remove residualmoisture of the fiber mesh. At block 430, monomers or oligomers areapplied to the fiber mesh via a resin application die that is positionedatop the lower belt. At block 440, the fiber mesh and the appliedmonomers or oligomers are passed between the lower belt and an upperbelt of the double belt press mechanism to press the monomers oroligomers through the fiber mesh and thereby fully saturate the fibermesh with the monomers or oligomers. At block 450, the fully saturatedfiber mesh is passed through a curing oven that is configured topolymerize the monomers or oligomers as the fiber mesh is moved throughthe curing oven and thereby form the thermoplastic polymer. The fibermesh is fully impregnated with the thermoplastic polymer uponpolymerization of the monomers or oligomers. The method may also includewinding the thermoplastic prepreg into a roll product or cutting thethermoplastic prepreg into sheets.

In some embodiments, the method may also include mixing the monomers oroligomers with a catalyst and an activator to form a reactive resinmixture. The catalyst and activator may facilitate in polymerizing themonomers or oligomers to form the thermoplastic polymer. The method mayalso include applying a moisture-free gas onto the fiber mesh after theapplication of the monomers or oligomers to substantially preventexposure of the monomers or oligomers to ambient moisture in thesurrounding environment. The top belt of the double belt mechanism maybe fully enclosed within the curing oven.

In some embodiment, the method may also include cutting fiber strands orrovings via a fiber chopper that is positioned above the lower belt toform the chopped fibers. The fiber chopper may be positioned so that asthe fiber strands or rovings are cut, the chopped fibers fall atop thelower belt and form the fiber mesh. In such embodiments, the method mayfurther include drying the fiber strands or rovings via a second dryingmechanism as the fiber strands or rovings are unwound from one or morespools and before the fiber strands or rovings are cut to form thechopped fibers.

The fiber chopper may be a first fiber chopper and the chopped fibersmay be first chopped fibers. In such embodiments, the method may alsoinclude cutting second fiber strands or rovings via a second fiberchopper that is positioned above the lower belt to form second choppedfibers. The second fiber chopper may be positioned so that as the secondfibers strands or rovings are cut, the second chopped fibers fall atopthe first chopped fibers and form a layered or hybrid fiber mesh.

The method may additionally include unwinding a fabric or nonwoven matfrom a roller and moving the fabric or nonwoven mat atop the lower beltso that the chopped fibers are positioned above or below the fabric ornonwoven mat and form a layered or hybrid fiber mesh that includes orconsists of the chopped fibers and the fabric or nonwoven mat. Thelayered or hybrid fiber mesh may be subjected to the drying mechanism,the resin application die, the double belt mechanism, and the curingoven so that the monomers or oligomers fully saturate the layered orhybrid fiber mesh and the thermoplastic polymer fully impregnates thelayered or hybrid fiber mesh upon polymerization of the monomers oroligomers.

In some embodiments, the method may additionally include applying asizing composition to the fibers of the fiber mesh. The sizingcomposition may have a coupling agent that promotes bonding between thefibers and the thermoplastic polymer. The fiber mesh may include glassfibers, carbon fibers, basalt fibers, metal fibers, ceramic fiber,natural fibers, synthetic organic fibers, aramid fibers, inorganicfibers, or combinations thereof. The monomers or oligomers may compriseor consist of lactams, lactones, cyclic butylene terephthalate (CBT),methyl methacrylate, precursors of thermoplastic polyurethane, ormixtures thereof. The lactams may comprise or consist of caprolactam,laurolactam, or mixtures thereof.

In some embodiments, a unidirectional tape may be coupled with at leastone side of the thermoplastic prepreg product formed according to themethod of FIG. 14. The unidirectional tape may be attached to a singleside of the thermoplastic prepreg or may be attached to both sides ofthe thermoplastic prepreg as desired. Coupling of the unidirectionaltape with the thermoplastic prepreg may be achieved in various ways. Forexample, the unidirectional tape may be laminated to one or both sidesof the thermoplastic prepreg. Alternatively, the thermoplastic prepregmay be positioned in a mold along with the unidirectional tape. Thethermoplastic prepreg and unidirectional tape may be stacked within themold in any desired configuration. For example, the thermoplasticprepreg may be sandwiched between two or more unidirectional tapes, orthe unidirectional tape may be sandwiched between two or more layers ofthe thermoplastic prepreg. Heat and pressure may be applied to theproducts within the mold to melt the thermoplastic materials and therebymold, weld, or otherwise couple the unidirectional tape(s) andthermoplastic prepreg(s) together. The mold may be in the shape of adesired final product so that the materials are simultaneously formedinto a desired shape and coupled together. Various other means ofcoupling a unidirectional tape to a thermoplastic prepreg arecontemplated herein.

Forming Composites from a Thermoplastic Prepreg

The thermoplastic prepregs may be formed into composite products viadifferent composite manufacturing processes, including but limited to,compression molding, thermoforming, stamping, injection overmolding, andlamination. In addition, thermoplastic prepregs may be combined withother composite sheet materials to form composite products. For example,as described herein, thermoplastic prepregs may be combined withunidirectional tapes via a lamination process to form hybrid laminates.In other embodiments, thermoplastic prepregs and unidirectional tapesmay be compression molded together to form composite products, withoutprior lamination or consolidation. In some embodiments, a compositeproduct may include a thermoplastic prepreg and a unidirectional tapethat is positioned on a first side of the thermoplastic prepreg. Thecomposite products may also include an additional unidirectional tapethat is positioned on a second side of the thermoplastic prepreg, inwhich the second side is opposite the first side. The thermoplasticprepreg may be formed via any of the systems or methods describedherein. Incorporating one or more unidirectional tapes with thethermoplastic prepreg can enhance load bearing capacity of the hybridcomposites.

Exemplary Materials and Systems

Uni-directional stitched fabric consisting of 1200 tex glass fiberrovings with the area weight of 670 g/m² were used for makingpolyamide-6 prepregs, using the system shown in FIG. 1A. Two heatedtanks were used for melting caprolactam-catalyst andcaprolactam-activator separately. 1,000 grams of caprolactam(Bruggemann, AP Nylon grade) and 74.0 grams of Bruggolen® C10 catalyst(containing sodium caprolactamate) were added to the first tank. Themixture of caprolactam and C10 was melted at 100° C. Separately, 1,000grams of caprolactam (Bruggemann, AP Nylon grade) and 27.0 grams ofBruggolen® C20 activator (containing N,N′-hexane-1,6-diylbis(hexahydro-2-oxo-1H-azepine-1-carboxamide)) wereadded to the second tank. The mixture of caprolactam and C20 was meltedat 100° C. The melts from the two tanks were then mixed at 1:1 ratio ina mixer before the application of the reactive resin mixture on thefabric through a slot die with the opening of 0.33 mm.

A double belt press oven with two Teflon-coated belts was used in theexperiments to press and cure the reactive resin mixture. The doublebelt press was electrically heated and the oven temperature was set at390° F. The line speed was set such that the residence time of thecoated fabric in the oven was approximately 3.5 minutes. The resinapplication rate was adjusted to achieve a target resin content of 30%in the prepregs.

Example 1

The experiment was run without infrared (IR) heating as shown in FIG.1A. The residual moisture on the fabric negatively impacted the anionicpolymerization of caprolactam. A significant amount of caprolactam fumewas observed at the exit of the double belt press oven; and sticking ofthe coated fabric to the belts was observed. The caprolactam fume at theoven exit indicates an incomplete polymerization of caprolactam.

Example 2

The experiment was run with IR heating and the fabric was heated to thetemperature of 330° F. prior to the application of the reactive resinmixture. The slot die was placed about 10 inches away from the inlet ofthe oven. No nitrogen purging or box enclosure was used to prevent theexposure of the coated fabric to ambient moisture. A significant amountof caprolactam fume was observed at the exit of the double belt pressoven; and sticking of the coated fabric to the belts was observed. Thecaprolactam fume at the oven exit indicates an incomplete polymerizationof caprolactam.

Example 3

The experiment was run with IR heating and the fabric was heated to thetemperature of 330° F. prior to the application of the reactive resinmixture. The slot die was placed within 1.0 inch from the inlet of theoven. Nitrogen was blown onto the coated fabric through perforated holeson a stainless steel tube, to prevent the exposure of the coated fabricto ambient moisture. Complete polymerization was achieved and minimalamount of caprolactam fume was observed at the exit of the double beltpress oven. No sticking of the coated fabric to the belts was observed.Scanning electron microscopy (SEM) analysis was conducted on theresulting prepregs to examine the impregnation. FIG. 4 is a typical SEMmicrograph of the cross-section of the prepreg, which indicates thecomplete impregnation of the fabric with thermoplastic polyamide-6resin.

As will be readily understood by a person of skill in the art, theresidual monomer or oligomer content in the prepreg can be measured viaa solvent extraction method. For example, to measure the amount ofresidual monomer in polyamide-6 prepregs, powder samples may be preparedby cryo-grinding small pieces of prepregs in a grinder in the presenceof liquid nitrogen. Powder samples may then be extracted with water at150° C. using an Accelerated Solvent Extractor (ASE). The water in theextraction vials may then be evaporated in a turbo evaporator at 65° C.under a stream of nitrogen. The residues may be dried in a vacuum ovenat 55° C.; and then weighed to determine the amount of extractedmonomer. The conversion rate may be calculated based on the amount ofthe extracted residual monomer and the starting amount of monomer thatis used for the impregnation.

“ASTM” refers to American Society for Testing and Materials and is usedto identify a test method by number. The year of the test method iseither identified by suffix following the test number or is the mostrecent test method prior to the priority date of this document. For anyother test method or measurement standard defined or described herein,the relevant test method or measurement standard is the most recent testmethod or measurement standard prior to the priority date of thisdocument. Where a range of values is provided, it is understood thateach intervening value, to the tenth of the unit of the lower limitunless the context clearly dictates otherwise, between the upper andlower limits of that range is also specifically disclosed. Each smallerrange between any stated value or intervening value in a stated rangeand any other stated or intervening value in that stated range isencompassed. The upper and lower limits of these smaller ranges mayindependently be included or excluded in the range, and each range whereeither, neither, or both limits are included in the smaller ranges isalso encompassed within the invention, subject to any specificallyexcluded limit in the stated range. Where the stated range includes oneor both of the limits, ranges excluding either or both of those includedlimits are also included.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a method” includes aplurality of such methods and reference to “the glass fiber” includesreference to one or more glass fibers and equivalents thereof known tothose skilled in the art, and so forth. The invention has now beendescribed in detail for the purposes of clarity and understanding.However, it will be appreciated that certain changes and modificationsmay be practice within the scope of the appended claims.

Also, the words “comprise,” “comprising,” “include,” “including,” and“includes” when used in this specification and in the following claimsare intended to specify the presence of stated features, integers,components, or steps, but they do not preclude the presence or additionof one or more other features, integers, components, steps, acts, orgroups.

What is claimed is:
 1. A system for manufacturing a thermoplasticprepreg, the system comprising: a double belt mechanism that includes anupper belt and a lower belt, the upper belt being positioned atop thelower belt so as to compress a fiber mat, web, or mesh that is passedthrough the double belt mechanism and the lower belt having alongitudinal length that is substantially longer than the upper belt; aresin applicator that is positioned atop the lower belt and that isconfigured to apply monomers or oligomers to the fiber mat, web, or meshas the fiber mat, web, or mesh is moved past the resin applicator,wherein the monomers or oligomers are polymerizable to form athermoplastic polymer; and a curing oven that is configured to effectpolymerization of the monomers or oligomers and thereby form thethermoplastic polymer as the coated fiber mat, web, or mesh is movedthrough the curing oven; wherein the double belt mechanism compressesthe fiber mat, web, or mesh and the applied monomers or oligomers as thefiber mat, web, or mesh is passed through the curing oven such that themonomers or oligomers fully saturate the fiber mat, web, or mesh and thefiber mat, web, or mesh is fully impregnated with the thermoplasticpolymer upon polymerization of the monomers or oligomers.
 2. The systemof claim 1, further comprising a gas application mechanism that ispositioned to blow a moisture-free gas onto of the coated fiber mat,web, or mesh in order to substantially prevent exposure of the monomersor oligomers to ambient moisture in a surrounding environment.
 3. Thesystem of claim 1, further comprising a drying mechanism that ispositioned atop the lower belt and that is configured to remove residualmoisture from the fiber mat, web, or mesh as the fiber mat, web, or meshis moved past the drying mechanism.
 4. The system of claim 1, furthercomprising a cooling mechanism that is configured to cool thethermoplastic prepreg after polymerization of the monomers or oligomers.5. The system of claim 1, further comprising a fiber chopper or a fiberscattering device positioned above the lower belt, the fiber chopper orfiber scattering device being configured to disperse fiber strands orrovings atop the lower belt to form the fiber mat, web, or mesh.
 6. Thesystem of claim 1, further comprising a twin-screw extrusion devicehaving a port that receives a powder or pellet material including themonomers or oligomers, wherein the twin-screw extrusion device isconfigured to melt and mix the powder or pellet material and deliver themelted material to the resin applicator.
 7. The system of claim 6,wherein the twin-screw extrusion device and the resin applicator areheated to maintain a temperature of the monomers or oligomers above amelting point of the monomers or oligomers prior to applying themonomers or oligomers to the fiber mat, web, or mesh.
 8. The system ofclaim 1, further comprising a roller around which a roll of a fabric,nonwoven mat, or unidirectional tape is positioned, wherein the systemis configured to unwind the fabric, nonwoven mat, or unidirectional tapefrom the roller and to move the fabric, nonwoven mat, or unidirectionaltape atop the lower belt.
 9. The system of claim 1, wherein the fibermat, web, or mesh includes glass fibers, carbon fibers, basalt fibers,metal fibers, ceramic fiber, natural fibers, synthetic organic fibers,aramid fibers, inorganic fibers, or combinations thereof.
 10. The systemof claim 1, further comprising a cutting mechanism that cuts thethermoplastic prepreg into sheets, the cutting mechanism beingpositioned after the curing oven.
 11. The system of claim 1, wherein themonomers or oligomers comprise lactams, lactones, cyclic butyleneterephthalate (CBT), methyl methacrylate, precursors of thermoplasticpolyurethane, or mixtures thereof.
 12. The system of claim 11, whereinthe lactams comprise caprolactam, laurolactam, or mixtures thereof. 13.The system of claim 1, wherein the monomers or oligomers include atoughening agent that is configured to toughen the thermoplasticprepreg.
 14. The system of claim 13, wherein the toughening agentcomprises a rubber material.
 15. A method of forming a composite productcomprising: providing the thermoplastic prepreg of claim 1; and couplinga unidirectional tape to at least one side of the thermoplastic prepreg.16. The method of claim 15, wherein coupling the unidirectional tape tothe at least one side of the thermoplastic prepreg comprises laminatingthe unidirectional tape to the at least one side of the thermoplasticprepreg.
 17. The method of claim 15, wherein coupling the unidirectionaltape to the at least one side of the thermoplastic prepreg comprisescompression molding the unidirectional tape to the at least one side ofthe thermoplastic prepreg.
 18. A composite product comprising: thethermoplastic prepreg of claim 1; and a unidirectional tape that ispositioned on a first side of the thermoplastic prepreg.
 19. Thecomposite product of claim 18, further comprising an additionalunidirectional tape that is positioned on a second side of thethermoplastic prepreg, wherein the second side is opposite the firstside.
 20. A method of forming a thermoplastic prepreg comprising: movinga fiber mat, web, or mesh atop a lower belt of a double belt pressmechanism; applying monomers or oligomers to the fiber mat, web, or meshvia a resin applicator that is positioned atop the lower belt; passingthe fiber mat, web, or mesh and the applied monomers or oligomersbetween the lower belt and an upper belt of the double belt pressmechanism to press the monomers or oligomers through the fiber mat, web,or mesh and thereby fully saturate the fiber mat, web, or mesh with themonomers or oligomers; and passing the fully saturated fiber mat, web,or mesh through a curing oven that is configured to polymerize themonomers or oligomers as the coated fiber mat, web, or mesh is movedthrough the curing oven and thereby form the thermoplastic polymer;wherein the fiber mat, web, or mesh is fully impregnated with thethermoplastic polymer upon polymerization of the monomers or oligomers.21. The method of claim 20, further comprising mixing the monomers oroligomers with at least one of a catalyst or an activator to form areactive resin mixture, the catalyst and activator facilitating inpolymerizing the monomers or oligomers to form the thermoplasticpolymer.
 22. The method of claim 20, further comprising applying amoisture-free gas onto the fiber mat, web, or mesh after application ofthe monomers or oligomers to substantially prevent exposure of themonomers or oligomers to ambient moisture in the surroundingenvironment.
 23. The method of claim 20, further comprising drying thefiber mat, web, or mesh via a drying mechanism that is positioned atopthe lower belt to remove residual moisture from the fiber mat, web, ormesh.
 24. The method of claim 20, further comprising dispersing choppedfibers atop the lower belt, via a fiber chopper or fiber scatteringdevice, to form the fiber mat, web, or mesh.
 25. The method of claim 20,further comprising passing the thermoplastic prepreg through a coolingmechanism after polymerization of the monomers or oligomers.
 26. Themethod of claim 20, further comprising unwinding a fabric, nonwoven mat,or unidirectional tape from a roller and moving the fabric, nonwovenmat, or unidirectional tape atop the lower belt.
 27. The method of claim20, wherein the fiber mat, web, or mesh includes glass fibers, carbonfibers, basalt fibers, metal fibers, ceramic fiber, natural fibers,synthetic organic fibers, aramid fibers, inorganic fibers, orcombinations thereof.
 28. The method of claim 20, further comprisingadding a toughening agent to the monomers or oligomers to toughen thethermoplastic prepreg.
 29. The method of claim 28, wherein thetoughening agent comprises a rubber material.
 30. The method of claim20, further comprising cutting the thermoplastic prepreg into sheets.31. The method of claim 20, wherein the monomers or oligomers compriseslactams, lactones, cyclic butylene terephthalate (CBT), methylmethacrylate, precursors of thermoplastic polyurethane, or mixturesthereof.
 32. The method of claim 31, wherein the lactams comprisecaprolactam, laurolactam, or mixtures thereof.
 33. The method of claim20, further comprising coupling a unidirectional tape with at least oneside of the thermoplastic prepreg.
 34. The method of claim 33, whereincoupling the unidirectional tape with the at least one side of thethermoplastic prepreg comprises: positioning the unidirectional tape onthe at least one side of the thermoplastic prepreg; and laminating theunidirectional tape to the at least one side of the thermoplasticprepreg.
 35. The method of claim 33, wherein coupling the unidirectionaltape with the at least one side of the thermoplastic prepreg comprises:positioning the thermoplastic prepreg in a mold; positioning theunidirectional tape on the at least one side of the thermoplasticprepreg within the mold; and applying heat and pressure to theunidirectional tape and thermoplastic prepreg to mold the unidirectionaltape to the at least one side of the thermoplastic prepreg.
 36. Acomposite product comprising: the thermoplastic prepreg of claim 20; anda unidirectional tape that is positioned on a first side of thethermoplastic prepreg.
 37. The composite product of claim 36, furthercomprising an additional unidirectional tape that is positioned on asecond side of the thermoplastic prepreg, wherein the second side isopposite the first side.